U-boat Archive - ASWORG Report 27



	ASWORG/87 – 1

	1 April 1944.



	RESEARCH REPORT 27

	ANTI-SUBMARINE OPERATIONS BY CVE BASED AIRCRAFT.


	ABSTRACT


	A detailed study of A/S operations by CVE based A/C covering the period March 1943 to February 15, 1944 is presented. Included are limited data on CVE operations: the Task Group; convoy coverage; U/B search; effect of weather and sea conditions; A/C handling and storage; speed and endurance of A/C; communications; armament; a typical day’s flight operations; details pertaining to U/B sightings; the attack; coverage and effectiveness of search plans and sweeps. A tabulation of the results is given in Table I. The dependence of surprise on altitude is quite marked, although there is no appreciable gain in probability of sighting with increasing altitude. CVE based A/C coverage is such that on a single sweep there is, on the average, a 50-50 chance of sighting a surfaced U/B which is present somewhere within the limits of visibility as viewed from the A/C.





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ASWORG/87 – 2

1 April 1944.

INDEX

	Abstract		1
	Table I. Summary of Sighting Statistics		3

PART A

	Introduction		6
		The CVE's general features	9
		Launching and landing planes	9
	Operations
		The flight deck	10
		Factors limiting operations	12
		Other A/S equipment with the task group	20
		A typical day’s Flight operations	21

PART B
	Operating statistics		23
	U/B sightings by CVE borne A/C		23
	U/B trim at time of sighting and cause of sighting		27
	Factors governing degree of surprise in making
		attack	29
	U/B response to attack		31

PART C

	Effectiveness of CVE based A/C search		33

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ASWORG/87 – 3

1 April 1944.

TABLE I
SUMMARY OF SIGHTING STATISTICS

Number of occasions when A/C sighted U/B					58

	Flying search			48
	Flying A.E.P. #15			4
	Investigating HF/DF			1
	Flying to relieve			2
	Mission not known			3

Number of U/B’s sighted					68

	Fully surfaced			53
	Diving trim			9
	Breaking surface			4
	Periscope depth			1
	Submerged			1

Number of U/B’s attacked					60

	Complete surprise to U/B			28
	Resulting in:	10A, 4B	50%
		3D	11%
		3E, 6F, 2G	39%

	Partial surprise to U/B			22
	Resulting in:	2A, 7B	41%
		4D	18%
		2E, 3F, 4G	41%

	No surprise to U/B			10
	Resulting in:	2A, 3B	50%
		1D	10%
		2E, 1F, 1G	40%

	TOTAL			60
		14A, 14B	47%
		8D	13%
		7E, 10F, 7G	40%

Evasive action - first attack				31

	AA fire		25
	Crash Dive		6

No evasive action – first attack				29

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ASWORG/87 – 4

1 April 1944.

TABLE I. (Continued)

	U/B sunk as a result of first attack	8
	U/B not seen after first attack	6
	U/B crash dive after first attack	18
	U/B remained surfaced – AA fire	28

Number of U/B’s escaping attack			8

	While A/C engaged with another U/B	6
	By crash dive	2

Number of CVE cruises			24 ½

Number of CVE days in U/B waters			680

ABD assessments per cruise			1.5

ABD assessments per day			0.053

Number of plane-hours flown			34,700

Number of plane-hours per sighting			600

Number of plane-hours per sighting
	for land based planes in Bay of Biscay (1943)		101

Number of plane-hours per A or B assessment			1,240

Number of plane-hours per A or B assessment
	for land based planes in Bay of Biscay (1943)		1,390

Average visibility in miles			12.3

	For complete surprise	12.2
	For partial surprise	12.9
	For no surprise	10.4

Average altitude for sighting surfaced U/B			3,350

	For complete surprise	4140
	For partial surprise	2860
	For no surprise	2000

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ASWORG/87 – 5

1 April 1944.

TABLE I. (Continued)

Average sighting distance for fully surfaced U/B					7.8

	For complete surprise			7.9
	For partial surprise			9.6
	For no surprise			4.7

Number of fully surfaced U/B’s sighted by wake					25

Number of fully surfaced U/B’s sighted by hull or C/T					27

Average state of sea for sighting surfaced U/B’s					1.9

	Sea state	0, 1	18
	“ “	2.	11
	“ “	3.	15
	“ “	4.	11

Average altitude of sighting partially surfaced U/B					2160

Average sighting distance for “ “					4.0

Average state of sea for sighting “					2.4

Average value of lateral distance W/V for surfaced U/B					0.38

Average value for W/V for partially surfaced U/B					0.26

Average distance from CVE to U/B					53.6

Average speed of U/B (in knots) at sighting					10.0

Average bearing of U/B relative to A/C				4⁰ to port

	23 sightings to port, average angle of 65⁰

	25 sightings to starboard, average angle of 47⁰

	6 sightings dead ahead

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	ASWORG/87 – 6

	1 April 1944.

	PART A

	INTRODUCTION

	Returning from a late afternoon patrol on 28 April 1943, a TBF from the USS BOGUE sighted and attacked a U/B at latitude 45⁰23’N, longitude 27⁰26’W. Although the U/B escaped without leaving evidence of damage, this action was the curtain raiser for a long series of actions between CVE based planes and U/B’s which have contributed materially to the great loss of effectiveness of U/B warfare in the mid-Atlantic.

	In all, 60 U/boats were subjected to attack between March 1943 and 15 February 1944 by CVE-based aircraft alone. Numerous other U/boats were attacked by the CVE’s escorts, sometimes alone, sometimes coordinated with aircraft. Not only has the U/boat activity decreased but those that remain have become exceedingly wary. U/boats are now spending less of their time on the surface during daylight in the mid-Atlantic.

	As a single example of what this victory has meant to our supply lines, consider the case of the UGS and GUS convoys to North Africa and the Mediterranean. These convoys operate in the mid-Atlantic and since May 1943 have been covered or supported by the CVE Task Groups. During this period to the end of 1943, 2237 merchantmen crossed the Atlantic in UGS and GUS convoys. Only one of those ships was lost due to U/boat action. Not another ship was damaged by this cause. Contrast this with 26 U/boat kills by CVE-based A/C alone during the same period.

	The CVE with her screen of 3 or 4 destroyers (recently raised to 5 destroyers) composes a Task Group, assigned to ASW in the Atlantic. The main purpose of the Task Groups is two fold: (1) to provide aerial coverage for Task Forces escorting convoys, in order to protect the convoy from U/boats approaching on the surface, and (2) to search out and destroy enemy submarines. Incidental to this is the interception and capture or destruction of enemy surface craft, particularly blockade runners.

	The great success of CVE’s in ASW operations is due to their ability to bring both F4F fighter planes and TBF

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	ASWORG/87 – 7

	1 April 1944.

	bombers directly to the heart of the U/boat concentrations. The CominCh Daily Estimates of U/boat positions have proven most reliable in predicting the location of these concentrations. Initially, the presence of planes in the mid-Atlantic was such a surprise that the U/boats were a long time in getting over it. In nearly half the attacks the U/boats were so surprised that they were not able to fight back until after the initial attack was delivered.

	Customary procedure is for the CVE to be with the convoy while passing through areas where U/boats are suspected. While in areas where no U/boats are suspected, the Task Groups will leave the convoy and head for concentration areas, there to conduct offensive sweeps. As the situation developed, with U/boats molesting convoys less and less, the trend was to spend an increasing proportion of the time on offensive sweeps.

	For protection of the convoy and of the Task Group when away from the convoy, Aerial Escort Plan No. 15 or a slight modification of it is used. So tight is this plan that a U/boat surfacing within 25 or 30 miles of the convoy will be sighted within half an hour at the most, and on the average within 15 minutes of the time of surfacing. Likewise it would be unusual for a U/boat to be able to move in on the surface to closer than 20 miles. In general, a surfaced U/boat would be sighted by the A/C before he can get close enough to the convoy to sight it. The fact that only one ship out of 2237 was attacked bears testimony to the effectiveness of Plan 15. On offensive sweeps large areas can be swept over in a day. A single CVE has put as many as 51 planes in the air in one day. A track chart for these planes would include an area of 18,500 sq. mi. within one mile of one of these tracks and an area of 90,000 sq. mi. within five miles. This means that any U/boat in an area equal to the combined areas of Connecticut, Rhode Island, Massachusetts and New Hampshire would have a plane pass within a mile of it, and any U/boat in an area half the size of California would be passed at less than five miles.

	The plans for offensive sweeps vary from ship to ship. However, they all possess the general common characteristic that different fighter-bomber teams each cover a given radial sector. The planes fly radially out from 40 to 100 miles (depending on plan used) then fly a cross-over of 10 to 30 miles, then directly in along a radius to intercept the CVE.

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	ASWORG/87 – 8

	1 April 1944.

	This plan might be better understood if one uses the analogy of movement out along the spokes of a wheel. The CVE is the hub, a team composed of a TBF and an F4F will sweep out the area enclosed by two adjacent spokes and the portion of the rim joining them. The motion is out along a spoke to the rim, then along the rim to the next spoke, and in along it. The area covered also includes that immediately outside the spokes and rim.

	Having once established contact with a U/boat the fighter bomber teams swing into a coordinated attack, at the same time breaking radio silence to give the CVE range and bearing of the action. The F4F goes in first for a strafe. The purpose of this is to distract the U/boats gun crews and thus enable the TBF to press home a low altitude depth charge attack without being shot down. The TBF follows close in behind the F4F but usually at an angle to its course. Except for the rarely encountered AA boats, the U/boat is no match for the F4F’s fire power. Prisoners of war have expressed their great fear and general feeling of hopelessness after being submitted to their first strafing from an F4F. The usual consequence of a single strafe or a series of strafings is the shooting up of both the guns and the gun crews, setting the ready box on fire, and puncturing of oil tanks, so that oil leaks out. A sufficient number of F4F’s are not always available for making the sweep, in which case the TBF is alone.

	While the initial attack is being carried out, the CVE is sending an attack group of F4F’s and TBF’s to the scene. Aircraft from adjacent sectors are also directed to teh scene. The attack group is always standing by in a state of readiness while the patrols are out on a sweep. They are launched and to the scene in a matter of minutes, providing the CVE received the attack message clearly. Communications failures are disastrous at this point so a careful checkup on equipment is made as soon as patrol planes get into the air. If the message is promptly and clearly received actions even as far as 100 miles away can be reached by the killer group within half an hour of receipt of the message. Shorter trips are made in correspondingly less time.

	Once the U/boat has been sunk or otherwise forced under, surface craft are sent to the scene (unless other extenuating circumstances make such a move impracticable) and hold-down and gambit tactics are entered into. It was just such an activity that led the USS BORIE to her famous action with U/boats. Such coordinated action of fighter and bomber,

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	ASWORG/87 – 9

	1 April 1944.

	patrol planes, and killer groups, aircraft and surface craft, has resulted in the high ratio of kills and damaging attacks.

	The CVE’s General Features

	The CVE’s of interest to this study are: the USS BLOCK ISLAND – CVE 21, BOGUE – CVE 9, CARD – CVE 11, CORE – CVE 13, CROATAN – CVE 25, GUADALCANAL – CVE 60, and SANTEE – CVE 29. The SANTEE is a converted oiler of about 24,000 tons displacement, overall length of 552 feet, 75-foot beam, draft 18 feet and a speed of 18 knots. Except for the GUADALCANAL, the others are constructed on the Maritime Commission Mercantile hulls, having a displacement of about 14,300 tons, overall length of 500 feet, 69 foot beam, draft 25 feet, maximum speed of 18 knots and an economical speed of 12 knots. The flight deck and gun sponsons have increased the overall beam of the CVE’s to about 110 feet. The flight deck on the SANTEE is about 500 feet long and 85 feet wide, whereas the others have a flight deck about 440 feet long.

	Launching and Landing Planes

	The first planes off are catapulted. The catapult officer directs the pilot, “reving the prop”, “checking the flaps”, and so on. When the plane is ready and at the moment the pitch of the ship is correct the plane is catapulted. The deck runs are more difficult as it is desirous to take off just as the end of the deck is pointing up, rather than down. This means that considerable judgment must be exercised in starting the plane off at the right moment. Also because of pitch part of the run must be made up hill. The runs are only about 450 feet, yet usually the planes leave the deck before reaching the end of the run. The planes are just above stalling speed as they leave the deck. On rare occasions one stalls into the water.

	Following the launching the planes are respotted. The ATTACK GROUP is put in position for launching, one plane being on the catapult. Other planes that need to be turned up, or have the wings tested are also spotted where they can be worked on. In case one of the planes just launched needs to return for an emergency landing – and this happens frequently during the early part of the trip before the planes have all the “bugs” worked out of them – it will be necessary to respot all of the planes that have just been spotted. The planes must be placed in the area forward of the barriers leaving the landing strip clear. After the emergency landing has been made, the planes are again respotted.

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	ASWORG/87 – 10

	1 April 1944.

	When all is in readiness for the landings, the flag signals go up and the bull horn is sounded. The first plane approaches the carrier in a long flat glide from the port quarter. AS it comes up astern of the carrier it is under the direction of the signal flags in the hands of the air landing officer, who is located on a platform on the port quarter of the landing strip. The pilot cannot always see the deck as he gets near to it. He relies on the guidance of the air landing officer, who is a pilot of extensive experience. If the landing signal officer is not sssatisfied with the manner in which the plane is coming in, he will give it a wave off. If the landing officer is satisfied with the plane’s approach, he continues to bring him in, and at the proper moment signals the pilot to “cut”. As a result of the cut the plane settles onto the deck. The tail hook picks up a pendant of the arresting gear and the plane is usually stopped within the next 50 to 80 feet.

	The actual landing is rather spectacular. The plane is coming in at very nearly a stalling speed. Slip streams from the ship have a marked effect on the plane. On some of the landings the planes come down rather hard. Tail wheels flying through the air are not an uncommon sight, and on rarer occasions a tire blows or landing gear collapses, and the plane skids along towards the side of the ship.

	After landing on the deck the plane is under the control of the deck officer. His crew rushes out, disengages the hook from the pendant and sees that the latter goes back into the plane. The pilot moves his plane according to the instructions signaled to him by the deck officer. In the case of the F4F’s the crew folds the wings. Wing folding on the TBF’s is automatic. The crew runs along with the plane to help push it around. All this action takes place rapidly and with fine coordination. After all planes are landed they are spotted and refueled. Those that are not needed above are taken below to the hangar deck – if there is room for them.

	OPERATIONS

	The Flight Deck

	The CVE’s originally carried F4F’s, SBD’s and TBF’s, but after a short trial the SBD’s were replaced by TBF’s.

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ASWORG/87 – 11

1 April 1944.

The TBF’s were considered superior to SBD’s in the attack because of the additional armament carried by the TBF’s and because the SBD’s wings do not fold, (hence occupying more space). The USS SANTEE carries a nominal complement of 20 TBF’s and 12 F4F’s. The other CVE’s have a nominal complement of 12 TBF’s and 6 F4F’s. These numbers vary somewhat from cruise to cruise but are fairly representative of a normal complement.

Some data pertaining to flight deck operations for the SANTEE are given in Table II. It is to be remembered that the flight decks for the other CVE’s are about 11% shorter. A plan view of the flight deck is given in Figure 1 and 2.

TABLE II

Length of flight deck			500 ½ ft.
Width of flight deck			85 ft.
Length of forward parking area.			106 ½ ft.
Length of usable parking area while
	planes are being catapulted		309 ½ ft.
Length of landing area aft of barriers			309 ½ ft.

Maximum stretch of barriers			30 ft.
Maximum stretch of pendants			145 ft.

Spacing of pendants		24 ft. to 29 ½ ft.
Number of pendants			9

Barrier breaking strength			92,400 lbs.
Pendant cable breaking strength			46,000 lbs.

Minimum wind velocity for
	full-load runway takeoff		25 kts.
Minimum wind velocity for
	catapult launching		16 ½ kts.

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	ASWORG/87 – 12

	1 April 1944.

	Factors Limiting Operations

	There are numerous factors which limit operations from the CVE. Aside from the military situation of the moment the most important are:

	1. Weather and sea conditions.
	2. Number of planes available.
	3. Plane handling and storage.
	4. Speed and endurance of planes.
	5. Pilot and observer fatigue.
	6. Communications.
	7. Armament carried by planes.
	8. Detection equipment.

	1. Weather and sea conditions. The effect of these elements on U/B sightings and attacks will be treated later on. However, the effect of weather and sea on launching and landing is worthy of discussion here. Landings are hazardous in a dead calm as the CVE is then barely able to produce the minimum wind velocity necessary for safe landings. The F4F’s in particular come in with such high speed relative to the deck that either a tail hook or a pendant may be severed. The TBF’s are liable to drop too suddenly at these low speeds and damage either a wheel or the landing gear. These hazards are usually considered minor.

	More hazardous are the conditions of a sea state of 4 or more combined with sharp, gusty winds. Here, one might have a serious accident because of a combination of deck rool, or pitch and a sudden change in wind speed. A rolling, pitching deck is hazardous for either launching or landing when strong, gusty winds are present. The plane is liable to get out of control on launching and to crash on landing. These operations are quite difficult for a sea state of 5, and nearly impossible for a seastate of 6. These conditions naturally cut down on the speed with which the deck crews can handle the plane. Worst of all is the case where icing conditions are added to the above. Here it is not unusual for the plane to go skidding across the deck completely out of control. At least one case is known where pilot and plane were lost overside while the plane was being taxied into position. A violent roll caused the plane to get out of control and skid along the ice until it went overside.

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	ASWORG/87 – 13

	1 April 1944.

	2. Number of planes available. This depends on the plane carrying capacity of the CVE, the number that are in mechanical operating condition, and of these, the number that are fueled up, loaded with machine gun bullets and depth charges. It is nearly impossible to satisfy all of the conditions simultaneously. Planes are lost at sea so the total number is diminished as the cruise progresses. It is unusual not to have at least one plane laid up for repair or overhaul. Two or three planes laid up is common and as many as six may be laid up on rarer occasions. Minor deck crashes involving broken wing and elevator tips, bent propellers, broken tail wheels and landing gear are comparatively common. It takes time to make these repairs. In order to place the planes back into service as soon as possible, repair shops operate with full complement 24 hours a day.

	Planes are inspected after each flight by Engineering Inspection Crews. The inspection includes landing gear for cracks and damages, bad tires, leaky oleo struts and damaged tail wheels, the hydraulic system, the arresting hook for operation and correct weight, the engine for oil leaks and loose spark plug leads. The planes have no regular overhaul period on board other than checks every thirty hours. On these checks, both plane and engine are given a thorough inspection for any trouble that has developed and for any item that may cause trouble in the future. All control cables are checked for wear; sheaves, for operation; hydraulic system gone over thoroughly. All operating parts are checked for proper functioning. Oil and spark plugs are changed on TBF’s every sixty hours. F4F’s get oil change every thirty hours and spark plugs change every sixty hours.

	Damaged elevators and rudders lead the list of repairs, with landing gear second. Leaking hydraulic actuating cylinders and timing valves are quite numerous. Repairs of a fairly extensive nature can be made on board ship. Propellers, motors, wheels, wings, elevators and rudders can be replaced. Most repairs on fuselage, landing gear and hydraulic system can also be made.

	Refueling takes place after each landing unless the plane is scheduled for the shop. The refueling is done on the flight deck whenever practicable. Otherwise it is done on the hangar deck. Planes that have had long warm-ups are “topped off” prior to flight. Thus when a plane returns, before it can take off again it must undergo an inspection, be refueled and have her supply of ammunition and depth

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	ASWORG/87 – 14

	1 April 1944.

	charges replenished. This is a time consuming task so the plane is not immediately available for action after landing.

	3. Plane handling and storage. This is one of the greatest and perhaps least appreciated problem of operations aboard the CVE. In a way it is reminiscent of the old Chinese checkers game, where, in order to move a particular piece nearly all the other pieces must be moved first. In the case of the CVE the problem is complicated by introducing another dimension. Planes are shuffled around on both the flight deck and the hangar deck, and the only way from one deck to the other is via two elevators.

	Figures 1 and 2 are scale drawings which indicate the amount of deck storage space available when planes are being landed when the catapult is not in use, and space available when catapulting. If no landings are being made, most of the space aft of the barriers is available for storage during catapult launchings. For deck launchings a row of planes may be stored on the starboard side as far forward as the barriers. A second row can be carried forward as far as the aft elevator.

	A maximum of 17 planes can be parked forward of the barriers. In case one of the first planes launched has to make an emergency landing, all the planes must be moved forward of the barriers. This can usually be worked out satisfactorily but it is time consuming. Not all of the planes can be stored on the hangar deck some of them must always be on the flight deck. The hangar deck plane capacity of the SANTEE is given in Table III. It is seen from the Table that from 11 to 16 of the SANTEE’s planes must be left on the flight deck.

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	ASWORG/87 – 15

	1 April 1944.



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ASWORG/87 – 16

1 April 1944.

TABLE III
HANGAR DECK PLANE CAPACITY OF THE USS SANTEE

TBF’s only		12

F4F’s only		26

TBF’s and F4F’s	12 TBF’s and 4 F4F’s
	9 “ 8 “
	6 “ 14 “
	3 “ 18 “

When the hangar deck is nearly full, plane handling is necessarily slower, particularly if there is a rough sea. The width of the hangar deck allows for the parking of three TBF’s abreast. This leaves just enough space between planes to maneuver them in and out. In rough seas this has been the contributing factor to numerous damaged plane elevators and rudders. The ships elevators are slow and will just take a TBF with very little room to spare. This also is a great handicap in rough seas and has contributed to a number of damaged plane elevators and rudders. The 8-ton hoists for lifting TBF’s are placed in such a position, relative to the elevators, that a TBF hoisted with wings spread practically immobilizes the elevator. Larger, faster elevators are desirable.

4. Speed and endurance of planes. The characteristics pertaining to the speed and endurance of TBF and F4F planes are given in Tables IV and V.

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ASWORG/87 – 17

1 April 1944.

TABLE IV
TBF

Gasoline capacity	301 gal.

Range at 150 knots	950 mi.

Endurance at 150 knots	6.3 hrs.

Cruising speed	150 kts.

Top speed	240 kts.

Minimum landing speed	70 kts.

TABLE V
F4F

Gasoline capacity

	a. Main plus emergency tanks		144 gal.
	b. Plus droppable wing tank		194 gal.
		(normal load)
	c. With two droppable wing tanks		244 gal.
		(Seldom used)

Range at 140 knots

	a. With 140 gal.		670 mi.
	b. With 194 gal.		850 mi.

Endurance at 140 knots

	a. With 144 gal.		4.7 hrs.
	b. With 194 gal.		6.0 hrs.

Cruising speed			135 kts.
Top speed (low altitude)			225 kts.
Minimum landing speed			68 kts.

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ASWORG/87 – 18

1 April 1944.

5. Pilot and observer fatigue. The constant strain of searching the ocean for U/B’s soon drains the observers zest for the sport. It seems that the efficiency of sighting decreases rapidly after about two and a half to three hours. Various factors affect the observers efficiency; such as the use of binoculars, sun glasses, condition of windshields, visibility, relative position of sun, condition of surface of sea, position in plane, amount of light, and vibration of plane. Clothing worn as well as parachute and fatigue of other parts of the body also are contributing factors. “Fanny Fatigue” begins to give trouble after about four hours.

6. Communications. Communication failure occurs with disturbing frequency. At least two U/B’s escaped possibly damaging attacks because communication could not be established until too late. There were numerous other instances when the communication failure was a serious nuisance. The equipment aboard the TBF’s and F4F’s are shown in Table VI.

TABLE VI

TBF-1C

	a. Transmitter ATC
	b. Receiver ARB
	c. ZB-3 (homing)
	d. ABK-3 (identification)

F4F-4

	a. Transmitter GF-1
	b. Receiver RU-18
	c. ZB-1
	d. ABK

A/C and CVE maintain radio silence until a contact with a U/B is made, or until the A/C is lost or under attack. Surface vessels intercepted by A/C are reported to the CVE by message drop, as are oil slicks and other objects that give a suspicious, but not positive indication of a U/B.

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1 April 1944.

ABK is to be on at all times, set for the code of the day. ZB is to be turned on only when a plane is lost or it is time to contact the carrier and the carrier is not in sight.

Usually an A/C reports the U/B as soon as it is sighted, although sometimes in the excitement and under the strain of establishing a state of readiness for the initial attack the transmitter is not turned on until after the initial attack. More often both receiver and transmitter get out of tune so the CVE receives either an incoherent message or nothing at all. The A/C does not receive the CVE’s request for a repeat of the message because his receiver is not in tune. Less frequently either the transmitter or receiver goes dead. In an attempt to minimize this effect tests are sometimes made with transmitters turned down low as soon as the A/C is launched and is in the immediate vicinity of the CVE. Operations would be improved if a more reliable transmitter and receiver were available.

7. Armament carried by planes. The armament carried aboard the TBF’s and F4F’s are shown in Table VII.

TABLE VII

TBF-1C

	a. 2 fixed .50 cal. Guns in wings, 310
		rounds each.
	b. 1 flexible .50 cal. Gun in turret, 400 rds.
	c. 4 Mark 47 depth charges.

F4F-4

	a. 6 fixed .50 cal. Guns in wings, 228 rds.
		each, loaded as follows:

		2 armor piercing, one tracer,
		2 armor piercing, one incendiary.

The .50 caliber guns fire 10 rounds per second. The depth charges are fused to explode at a depth of 25 feet.

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	ASWORG/87 – 20

	1 April 1944.

	As an alternative the TBF-1C can carry one torpedo, or twelve 100 lb. bombs or four 500 lb. bombs, or two 1000 lb. bombs. The 500 lb. bomb was tried by TBF’s from one carrier, but the results were not as good as to be expected from the use of depth charges.

	8. Detection equipment. TBF’s carry ASB-6 radar. No independent sightings were ever made with this instrument. In general its performance was considered somewhat unsatisfactory. This was due to three main causes: (a) the frequency for which the meters were calibrated did not correspond to the frequency of the generator, thus it was difficult to adjust to proper voltages for balancing, (b) the instruments were not sufficiently cushioned against shock and vibration, making it difficult to keep in tune, (3) radar training did not include what to do about such difficulties, so often enough the operator gave up in despair. By September there was sufficient evidence to indicate that German search receivers could detect ASB-6. This also coincided with the month in which only one U/B was attacked by a CVE based plane. As a result ASB-6 radar was not to be used unless the visual range was less than the radar range.

	TBF’s are now equipped with expendable radio sono-buoys. These are of particular value in investigating moving oil slicks, in tracking and for obtaining information of value in assessing the results of the attack. The use of sono-buoys was introduced but recently, as late as December, although trials had been made earlier.

	Still more recently some TBF’s have been equipped with rockets. The first attack using rockets was from the USS BLOCK ISLAND on 11 January. This was followed by the two attacks by A/C from the USS GUADALCANAL on 16 January. All three attacks were initiated with rockets, followed by depth charge attacks. Direct hits were believed scored on all three U/B’s.

	Some TBF’s are being fitted with searchlights. The extent of their usage is not known. Night flying from a CVE is particularly hazardous, also the landing will be more difficult.

	Other A/S Equipment with the Task Group

	The Task Group has other ASW equipment in addition to the A/C. The CVE has SG and SK radar, although the SK is

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	ASWORG/87 – 21

	1 April 1944.

	not used for U/B search. The CVE has HF/DF as does sometimes one of the escort destroyers. The destroyers have their normal complement of ASW weapons, depth charges, hedge-hog and gun fire, and radar and sonic detectors. There is no point on elaborating on this subject as it is already well known.

	A typical Day’s Flight Operations

	During the previous afternoon and night the flight schedule for the following day is made up. During the night the servicing crews condition the planes and spot them in proper position for takeoff routine. Two hours before sunrise the scheduled pilots for flight ABLE and the ATTACK GROUP have early breakfast and man the ready room. There, the pilots receive their instructions and weather reports. They work out their navigation and are ready to man their planes the instant they are called.

	General quarters are sounded just before dawn at which time the planes are warmed up. An half hour before sunrise flight ABLE is launched.

	As the time for landing flight ABLE approaches, Flight Quarters are sounded. The planes for flight BAKER are warmed up and launched. This flight usually consists of two planes, in addition are any other planes sent up for special purposes such as plane tests, or qualification landings for new pilots. After flight BAKER is in the air, the ATTACK GROUP planes, and others being worked on, are respotted ahead of the barrier in preparation of landing flight ABLE.

	As each plane of flight ABLE reported back to the ship, prior to landing, it would come up the starboard side with landing hook extended. When opposite the ship the pilot would wag the wings to indicate he had carried out the necessary condition of readiness preparatory to landing. He would then join the other planes in flying a landing circle about the ship. A blinker light signal is sent to the plane to land first. The others follow in order, including those just launched for qualification landings.

	The schedule for the complete day is given in Table VIII.

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ASWORG/87 – 22

1 April 1944.

TABLE VIII
AIR OPERATIONS SCHEDULE FOR FRIDAY, 24 SEPTEMBER 1943

STAND-BY KILLER GROUP – 4 TBF’s and 2 F4F’s.

0405 – FLIGHT ABLE and KILLER GROUP pilots man the Ready Room

0445 – GENERAL QUARTERS

0505 – (a) Launch Flight ABLE
	(1) A/S Scouting Patrol
		a. 4TBF’s and F4F’s to search 360⁰ to a
			distance of 100 miles
	(2) Convoy Escort
		a. Patrol Starboard - 1 TBF
		b. Patrol Port - 1 TBF

0845 – FLIGHT QUARTERS

0915 – (a) Launch Flight BAKER
	(1) Convoy Escort
		a. Patrol Starboard - 1 TBF
		b. Patrol Port - 1 TBF
(b) Land Flight ABLE

1300 – FLIGHT QUARTERS

1330 – (a) Launch Flight CHARLIE
	(1) A/S Scouting Patrol
		a. 6 TBF’s and 6 F4F’s to search the forward
			semi-circle to a distance of 150 miles
			and the after semi-circle to a distance of
			50 miles
	(2) Convoy Escort
		a. Patrol Starboard - 1 TBF
		b. Patrol Port - 1 TBF
(b) Land Flight BAKER

1715 – FLIGHT QUARTERS

1745 – (a) Land Flight CHARLIE

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	ASWORG/87 – 23

	1 April 1944.


	PART B

	OPERATING STATISTICS

	CVE’s have made 24 ½ cruises against U/B’s. During this time 680 days were spent in U/B waters and 34,700 plane hours were flown. The operating statistics are summarized in Table I.

	U/B SIGHTINGS BY CVE BORNE A/C

	The total sightings, attacks and coordinated actions are listed in Table IV. The first column gives the “sighting number” for the CVE in question; the second column, the U/B number; the third column, the attack number; the fourth column, the GCT; the fifth column, the date; the sixth column, the latitude; the seventh column, the longitude; the eighth column, the number of A/C involved; the ninth column, the assessment. Included are coordinated attacks with surface vessels which did not involve an independent sighting by the A/C.

	58 instances of sightings involving 68 U/B’s were made. 60 of the U/B’s were attacked, while 8 escaped by crash diving. Of the 8 that escaped, 6 did so while the A/C was engaged with a companion U/B. Only 2 escaped by crash diving before the A/C could press home an attack.

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ASWORG/87 – 24

1 April 1944.

TABLE IX

Sight No.	U/boat No.	Attack No.	Time	Date	Lat.	Long	No. A/C	Assessment

USS BLOCK ISLAND - CVE 21


1	1	1	0905	10/28	4853	3330	1	PA
	2	2	0905	10/28	4853	3330	1	PB
2	3	3	0920	1/11	4156	2053	2	PA


USS BOGUE - CVE 9


1	1	1	1840	4/28	4523	2726	1	F
2	2	2	2113	5/21	5200	3525	1	F
3	3	3	0634	5/22	5056	3350	1	E
4	4		0745	5/22	5200	3433	1	No attack
5	5	4	1058	5/22	5140	3347	1	D


6	6	5	1418	5/22	5055	3315	1	F
7	7	6	1840	5/22	5040	3521	2	A
8	8	7	1842	6/4	3228	4310	4	E
9	9	8	1914	6/4	3150	4321	2	F
10	10	9	1914	6/4	3258	4338	1	G


11	11	10	0845	6/5	3018	4250	2	B
12	12	11	1707	6/8	2907	3334	4	D
13	13	12	1345	6/12	3049	3349	8	A
14	14	13	0800	7/23	3328	2848	2	E
15	15	14	1402	7/23	3525	2756	1	A


	16		1402	7/23	3525	2756	1	No attack
16	17		1903	7/24	3426	2218	1	No attack
			1550	11/27	3852	1954	1	PJS*
			1545	11/29	3946	1906	1	PJS*
17	18	15	1550	11/29	3933	1901	4	PD


18	19	16	1740	11/30	4121	1819	1	D
			0950	12/1	4207	1910	2	D*
19	20	17	0927	12/12	2627	2944	5	PA
20	21	18	1539	12/20	3254	3701	1	A

USS CARD - CVE 11


1	1	1	1925	8/3	3635	4039	1	PD
2	2	2	0951	8/7	3932	3821	1	G
	3	3	1037	8/7	3932	3821	5	B
3	4	4	0800	8/8	4132	3828	2	D
	5		0800	8/8	4132	3828		No attack

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ASWORG/87 – 25

1 April 1944.

TABLE IX (continued)

Sight No.	U/boat No.	Attack No.	Time	Date	Lat.	Long	No. A/C	Assessment

USS CARD (continued)

			1943	8/8	4117	3840	1	F
4	6	5	1418	8/9	4212	3729	4	A
5	7	6	1613	8/11	4129	3855	2	A
6	8	7	1231	8/27	2844	3755	1	B
7	9	8	1307	8/27	2819	3758	3	B


8	10	9	1109	10/4	4313	2858	1	B
	11		1109	10/4	4313	2858	1	No attack
	12		1109	10/4	4313	2858	1	No attack
	13		1109	10/4	4313	2858	1	No attack
9	14	10	1709	10/4	4318	2858	1	B


10	15	11	1223	10/12	4923	3008	1	F
11	16	12	1451	10/12	4920	3007	1	F
12	17	13	1659	10/12	4950	2824	3	F
13	18	14	0935	10/13	4906	2947	1	G
15	20	16	1801	10/13	5014	2717	1	G


16	21	17	1541	10/30	4843	3219	1	G
17	22	18	1805	10/31	4914	3155	1	B
	23		1805	10/31	4914	3155	1	No attack

USS CORE - CVE 13

1	1	1	1624	7/13	2715	3418	5	A
2	2	2	1057	7/14	2733	3634	1	E
3	3	3	0911	7/16	3005	4417	1	A
4	4	4	1324	8/23	2804	3716	5	E
5	5	5	0837	8/24	2700	3706	3	A


6	6	6	1416	8/24	2709	3703	1	B
7	7	7	1545	10/20	4740	2827	1	B
8	8	8	0840	10/21	4657	2909	3	D
			1855	1/2	4505	1813	1	PJS*

USS CROATAN - CVE 25

1	1	1	1825	8/21	4205	2400	2	F
2	2	2	1326	9/9	3531	2552	1	F

USS GUADALCANAL - CVE 60


1	1	1	1845	1/16	4030	3720	1	PA
	2	2	1845	1/16	4030	3720	1	PA

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ASWORG/87 – 26

1 April 1944.

TABLE IX (continued)

Sight No.	U/boat No.	Attack No.	Time	Date	Lat.	Long	No. A/C	Assessment

USS SANTEE - CVE 29

1	1	1	1738	3/16	715	2917	3	E
2	2	2	0811	7/14	3354	2713	2	B
3	3	3	1832	7/14	3314	2656	2	G
4	4	4	2107	7/14	3317	2702	1	G
5	5	5	0824	7/15	3402	2602	2	B


6	6	6	1546	7/15	3152	2723	2	F
7	7	7	0824	7/24	3310	1954	2	D
8	8	8	1817	7/30	3457	3511	2	E
	9	9	1820	7/30	3457	3511	2	B

*Coordinated action with surface ship. No sighting.

SUMMARY

CVE	No. of Cruises	No. of Sight	No. U/B	No. Att.	No. A/C	Assessments

BLOCK IS.	2	2	3	3	3	2PA, 1PB

BOGUE	7	20	21	18	49	5A, 1B, 4D, 3E, 4F, 1G

CARD	4	17	23	18	37	2A, 7B, 2D, --, 3F, 4G

CORE	4	8	8	8	21	3A, 2B, 1D, 2E

CROATAN	3 1/2	2	2	2	3	--, --, --, --, 2F

GUADALCANAL	1	1	2	2	2	2A

SANTEE	3	8	9	9	16	--, 3B, 1D, 2E, 1F, 2G

TOTALS	24 1/2	58	68	60	130	14A, 14B, 8D, 7E, 10F, 7G

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ASWORG/87 – 27

1 April 1944.

U/B TRIM AT TIME OF SIGHTING AND CAUSE OF SIGHTING

Table X gives a summary of the U/B trim at the time of sighting. In two cases attention was first attracted by the U/B AA gun fire. An investigation of an oil slick revealed a U/B at periscope depth. Most unusual sighting of all was the observation of a submerged U/B as the A/C chanced to cruise over it.

Table XI gives a summary of the attraction that led to the sighting. The chief causes were the sighting of the wake and the sighting of the U/B itself. These two are about equally divided. In two cases the wake and the U/B were sighted simultaneously. The wake is more easily seen when the U/B is viewed end-on, although actually several factors are involved such as position of the sun, state of sea, cloud background and amount of haze, fog and rain. The bow waves were seen first in two of the cases where the U/B was sighted while breaking surface. Their remains little doubt that had the U/B’s not been sighted just as they broke surface that the conning tower would have been sighted shortly after anyway.

TABLE X
U/B TRIM AT SIGHTING

CVE	Fully surfaced	Diving trim	Breaking surface	Periscope depth	Sub-merged	TOTAL

BLOCK IS.	2					2

BOGUE	16	3	1			20

CARD	11	5	1			17

CORE	7			1		8

CROATAN	1	1				2

GUADALCANAL	1					1

SANTEE	5		2		1	8

TOTALS	43	9	4	1	1	58

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ASWORG/87 – 28

1 April 1944.

TABLE XI
CAUSE OF SIGHTING

CVE	U/B	Wake	Not Known	AA fire	Bow wave	TOTALS

BLOCK IS.	1	1				2

BOGUE	7	10	1	1	1	20

CARD	10	6	1			17

CORE	1	7				8

CROATAN	1			1		2

GUADALCANAL	1					1

SANTEE	6	1			1	8

TOTALS	27	25	2	2	2	58

For the 9 cases of U/B at diving trim it is certain that the U/B was not diving in 6 of the cases. In 3 cases the U/B crash dove, but not until the plane had the U/B in view for nearly a minute. Here again it is not certain that any of the U/B’s were actually in the process of diving when first seen. Some of the U/B’s may have been running with decks awash in order to present a smaller target for radar. Others may have done so in order to get away for a fast dive.

In view of the fact that none of the 58 sightings were made on a U/B which was positively diving when first sighted, and at the best there can be only 3 improbably diving cases, it is a little surprising that 4 U/B’s were caught in the act of surfacing. There are two alternative assumptions that can be made to explain this: (a) the planes were observing at a time of day when there was a greater proportion surfacing than submerging; (b) that the surfacing and submerging is more or less uniform (except at dawn and dusk) and instead of sighting 2 U/B’s surfacing and 2 submerging, the statistical fluctuation made it appear as no submergings a 4 surfacings.

For the case of assumption (a) the local times were: 0434, 1020, 1442, and 1845 – times which are well distributed

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	ASWORG/87 – 29

	1 April 1944.

	throughout the day. For the case of assumption (b), one takes 4 sightings as the sum of those where the U/B was either surfacing or submerging and an average of 2 each. Assuming one minute for surfacing or submerging, this would lead to an average time per U/B on the surface of only an hour. As judged from other information this time is far too short, indicating a disproportionately large number of U/B’s have been observed breaking surface.

	FACTORS GOVERNING DEGREE OF SURPRISE IN MAKING ATTACK

	Of particular interest is the element of surprise on the initial attack. There are several factors that might contribute to the surprise, such as visibility, sea, altitude, cloud cover, sun’s position, relative position of U/B and A/C, and distance of sighting. Insufficient data is available to evaluate the part played by the sun’s position. A high sea or rainy weather increases difficulties of observation by the U/B more than it does for the A/C. In rough and foul weather the lookout’s glasses are constantly being filmed with salt-water spray. The conning tower is weaving and bobbing in such a manner to make uniform scanning difficult. It should be more trying for the lookout to look in the direction of the sun, although the meager data available does not indicate this is an important factor. Low visibility seem to favor the U/B. It is equally difficult for the one to see the other, and as soon as the U/B is visible to the A/C the A/C is then close enough so that the U/B see him before he can take proper cover. The dependence of surprise on distance of sighting is linked with this. In general the smaller sighting distances go with the lower visibilities. This is illustrated in Table XII, where the average sighting distance is much less for no surprise than for complete surprise, although the ratios of distance of sighting divided by the visibility differ but very little.

	The most marked dependence is on altitude, although this again is indirectly linked with visibility (in general, low visibility means low altitude). However, the dependence on altitude is more clearly shown if one considers only those cases where the altitude was 5,000 feet or more.

	The statistics are given in Table XII for fully surfaced U/B’s only. The class 1 surprise is for the case that no evasive action of any sort was taken up until after the initial attack had been delivered. The class 2 surprise is for the case that no evasive action was indicated until the A/C was in position to deliver the attack. It is most

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ASWORG/87 – 30

1 April 1944.

likely that the A/C saw the U/B first in this case, but was not able to completely surprise the U/B. The average sighting distance for the class 2 surprise is 9.6 miles. If the U/B had seen the A/C first it is likely that it would have submerged. Instead, the U/B continued as it was until the A/C was within 1/2 mile to 2 miles of it. The class 3 surprise is for the case when the U/B definitely saw the A/C first. In Table XII, w is the perpendicular distance between the two parallel lines through the A/C and U/B, both of which are parallel to the course of the A/C.

TABLE XII

Class	No.	Vis.	Sea	Altitude	d	d/v	w/v

1	19	12.3	2.0	4140	7.0	.61	0.32

2	18	12.9	1.9	2860	9.6	.77	0.43

3	5	10.8	1.6	2000	4.7	.57	0.37

TOTALS	42	12.3	1.9	3350	7.8	.68	0.38

Table XIII shows the dependence of surprise on altitude for all sightings above certain altitudes. A steady increase in percentage of class 1 surprise is noted with increasing altitude. No U/B sighted the A/C first when A/C was at altitude greater than 5000 ft.

TABLE XIII

Altitude Range	No. in class
		1	2	3

5000-7500		8	3	0

2800-4900		6	3	1

0-2700		5	11	4

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ASWORG/87 – 31

1 April 1944.

The dependence of the A/C position with respect to the U/B is shown in Table XIV. It is to be noticed that although there is no marked relationship between angle of A/C and surprise, that more than twice as many sightings were made with the U/B viewed end on than were made with the U/B viewed beam on.

TABLE XIII

Angle of A/C meas. off beam	No. in class				Total
		1	2	3

0-30		8	3	0	9

31-90		6	3	1	13

61-90		5	11	4	19

The condition for greatest surprise does favor the end on approach slightly only on comparing class 3 with class 1 and 2. The comparison of class 2 and 3 together with class 1 favors the beam approach slightly. This indicates surprise to be only very slightly dependent on angle asa viewed from U/B, but the sightings in general without regard to element of surprise, are favored by an end on view.

A/C try to comply with A/S Warfare Doctrine for A/C in carrying out the attack, however extenuating circumstances prevent following it to the letter. The large percentage of class 1 surprise indicates that the Doctrine for approach after sighting is sound and is well carried out. Occasionally the initial run is spoiled by bombs hanging up, or because wrong settings are made. On rarer occasions the bombs are prematurely released. Still rarer are the occasions when the plane is damaged by AA gun fire. As shown in Table I, only 8 of 60 U/B’s were definitely sunk as a result of the initial attack. In 6 other cases the U/B was not seen after the initial attack. Of the 46 remaining U/B’s attacked, 18 immediately crash dived and 27 remained on the surface to fight it out.

U/B RESPONSE TO ATTACK

In all, 31 U/B’s took evasive action before, or as the initial attack was delivered. Of these, 25 engaged in AA

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	ASWORG/87 – 32

	1 April 1944.

	fire, while 6 went into a crash dive (but did not escape attack). In several instances the attacking A/C was engaged by two U/B’s. In general the A/C showed little regard for AA fire. In nearly every case that AA fire was encountered, the attack was pressed home regardless. Also, when the aircraft maneuvered for position for second attack they would usually keep close enough for the U/B to prevent it risking escape by diving. This meant the A/C was frequently within range of AA fire but by constantly changing altitude remained so with immunity.

	A curious aspect of the U/B countermeasures is their tendency to remain on the surface and fight it out. Actually, the longer they remain on the surface, the less chance they have. If he would only remain long enough every plane aboard the CVE would have a crack at him. Also, the longer he remains surfaced, the closer the surface vessel will be to him when he finally submerges, and the greater the chances that he will be so damaged that he will be in poor condition to resist destroyer depth charge attack. Prisoners of war state that when the U/B is surprised it is to remain on the surface and fight it out with the A/C. However, this is obviously not a good doctrine against CVE based A/C, because it would be only a matter of time until he had an entire Task Group on him.












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ASWORG/87 – 33

1 April 1944.

PART C

EFFECTIVENESS OF CVE BASED A/C SEARCH

The effectiveness of A/C search can be determined provided sufficient data are available. This has been discussed in detail in ASWORG Research Report No. 16. In order to determine if any marked relationship between the altitude and probability of sighting U/B’s exists, Table XV is presented, in which the function w/v (perpendicular distance from U/B to course of A/C divided by the visibility) is compared for different ranges of altitude.

TABLE XV

Altitude range	Average Altitude	No.	Vis.	d	d/v	w/v

0-2000	1370	12	9.8	7.3	.79	.38

2100-4000	2870	15	10.5	7.1	.65	.38

4100-7500	5570	14	16.4	8.9	.58	.35

TOTAL	3350	42	7.8	7.8	.68	.38

*Includes one sighting with altitude unknown

The average values of w/v over the three altitude ranges are constant within the limits of accuracy of their determination.

The value of w/v was computed for each sighting where sufficient data were available. The frequency distribution of the values of w/v over the ranges .00-.09, .10-.19, etc. are tabulated in table XVI.

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ASWORG/87 – 34

1 April 1944.

TABLE XVI
FREQUENCY DISTRIBUTION OF W/V

Range of w/v		N

.00-.09		7

.10-.19		6

.20-.29		4

.30-.39		9

.40-.49		4

.50-.59		1

.60-.69		3

.70-.79		2

.80-.89		2

.90-.99		2

A plot of these points (frequency versus w/v) show such a distribution that a straight line gives as good a fit as any of the standard types of distribution curves. In other words, the character of the data is such that a linear relationship between the variables will be true within the limits of uncertainty of data gathered for several months. This means that the error introduced by the application of the linear relationship to search plans for any one cruise will be considerably less than the inaccuracies of carrying out the search. The plot of the frequency distribution of w/v is shown in Figure 3.

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	ASWORG/87 – 35

	1 April 1944.




	ASWORG/87

	-35-



	ASWORG/87 – 36

	1 April 1944.

	The probability of sighting a surfaced U/B when an A/C approaches it and passes either directly over it or a few hundred yards to one side is taken to be very close to unity. Likewise, the probability of sighting a U/B at the limit of visibility and directly off the beam is taken to be very small, as the U/B, besides being at the limit of visibility remains there for only a few moments. This being the case, Figure 3 can be taken to represent the probability of sighting a surfaced U/B when passing within a perpendicular distance w of it at a time when the visibility is v.

	If one could see equally well everywhere within the limit of visibility as he can within the immediate vicinity of the A/C, the probability of sighting the U/B at all values of w up to v would be unity. Thus the coverage at any distance w is given by the ratio of probability of sighting a w to unity. If the probability of sighting as given in Figure 3 is multiplied by 100, one then obtains the coverage in percent.

	The percent of possible sightings out to a given distance w is given by summing the coverage for all distances out to w. The percentage of coverage out to different values of w is given in Figure 4.

	It is seen that half of the U/B’s sighted are at a perpendicular distance from the plane of only three-tenths of the visibility. 90% of those sighted are within seven tenths of the visibility.

	The average coverage out to a distance w is shown in Figure 5. At one-tenth of visibility the average coverage is 95%. At one-half of visibility the average coverage is 75% and clear out to the limit of visibility the average coverage is 50%. This means that when a single sweep is made, on the average only half of the surfaced U/B’s will be sighted.

	In order to sight a higher percentage it will be necessary to cover part of the same area again. This of course, entails more flying, so the search efficiency is reduced. In general, the higher the coverage, the less the efficiency, and the smaller the area that can be covered by a given number of planes.

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	ASWORG/87 – 36

	1 April 1944.



	ASWORG/87

	-37-

ASWORG/87 – 38

1 April 1944.

Table XVII gives the coverage that will result when a certain distance between parallel courses of the A/C is used. A distance of 2v means that the A/C goes out on a straight course and returns on a parallel course a distance twice the visibility away, a third course would be 2v away from the second, etc. Included in Table XVII are the distance the A/C must fly in order to give the indicated coverage, and the efficiency of the search in terms of coverage. The meaning of the efficiency of search may be illustrated by the following example: A CVE is to cover a certain area. Time is not available to give the highest coverage to the entire area, in fact just enough time is available to cover the area once with a path spacing of 2.0v. Now it is to be noticed that this path spacing gives only a 50% coverage, that is only a 50-50 chance of sighting the surfaced U/B if it is present. However, a path spacing of 0.5v gives a coverage of 97%, which allows the U/B only one chance in thirty to avoid detection, but, this path spacing will require 4 times the flying so only 25% of the entire area can be covered. This results in only a 25% coverage of the entire area, whereas the path spacing of 2v gives twice the coverage, or twice the chance that the U/B will be sighted.

TABLE XVII

Path Spacing	Coverage in %	Distance Flown	Efficiency of Search

2.0v	50	d	50%

1.5v	60	1.3d	45

1.2v	73	1.7d	44

1.0v	83	2.0d	42

0.8v	90	2.5d	36

0.6v	95	3.3d	28

0.5v	97	4.0d	25

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	ASWORG/87 – 39

	1 April 1944.

	As a general rule: if one has a situation that a certain area is to be searched and it is not known where in the area the U/B may be – just somewhere in it, then the best chance of sighting it will be given by using the path spacing which will just enable the entire area to be covered in the allotted flying time. Figure 6 gives the manor in which the coverage varies with path spacing.

	The radial section sweeps that CVE’s use are not the most efficient type of sweep to use. The most efficient type of sweep would be one of parallel paths perpendicular to the base course of the CVE. In sweeping through an area believed to contain a U/B concentration, the CVE should (and nearly always does in practice) set a course so that she is just outside the area at dawn. For her own protection she should have two planes flying Aerial Escort Plan #15, always remaining within 12 miles of the CVE. The sweeps should be made in parallel paths perpendicular to the base course of the CVE.







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	ASWORG/87 – 40

	1 April 1944.



	ASWORG/87

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	ASWORG/87 – 41

	1 April 1944.

	By way of illustration a detailed plan for a special case is given in Figure 7. The problem is to cover an area of 200 miles by 250 miles as best that can be done. The average visibility is 12 to 15 miles, 14 hours of daylight, 4 F4F’s and 10 TBF’s are available. A team of F4F’s and TBF’s fly out to 105 miles port and starboard from A. At the same time 2 TBF’s are put off to fly A.E.P. #15. 4 more TBF’s and 2 F4F’s are launched between A and B and the A flight is recovered between D and E. An extra flight of two TBF’s are put off between F and G to fly out ahead of the area before sundown. All planes are recovered at H just after sundown. Each plane flies 440 mi., or 3 hour time on the plan. During this time the group advances 48 miles. The average coverage will be about 70%. The forward sweep from F and G requires only about 2 hours of flying. These times permit investigation of suspicious objects. On the back sweep the planes come within 12 miles of the CVE, thus permitting message drops if necessary without serious loss of flying schedule.



	Submitted by:


	W. E. ALBERTSON
	ASWORG




	Approved by:


	G. E. KIMBALL
	ASWORG

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	ASWORG/87 – 42

	1 April 1944.



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