U-boat Archive - Interrogation of U-Boat Survivors

SECTION II. GERMAN U-BOAT COMMUNICATIONS

(i) Anglo-German Equivalent Wave Ranges.

As the German nomenclature of wave ranges is different from that of the Allies (fact), it is given here for convenience:

			Approximate Allied equivalents used in this report:
Laengstwelle	Below 100 kc/s	Very long wave	Very low frequency (VL/F)
Langwelle	100-1,500 kc/s	Long wave	Medium frequency (M/F
Grenzzwelle	1,500-3,000 kc/s	Intermediate wave
Kurzwelle	3,000-30,000 kc/s	Short wave	High Frequency (H/F
Ultrakurzwelle	Above 30,000 kc/s	Very short wave	Very high frequency (VH/F)

"Ultrakurzwellen" are subdivided into:

Meterwelle	Metre wave
Dezimeterwelle	Decimetre wave
Zentimeterwelle	Centimetre wave

(ii) W/T Equipment.

All U-boats carry the following or similar W/T gear:

(a) W/T Transmission.

(1) 1 Telefunken H/F transmitter 200 watt, frequency range 3.75 to 15 mc/s. S 406 S.

(2) 1 Telefunken M/F transmitter 150 watt, frequency range 300 to 600 kc/s. Spez. 2113 S.

(3) 1 Lorenz H/F transmitter 40 watt, frequency range 5 to 16.7 mc/s. 40 K 39 a.

(4) No R/T transmitter usually carried on operations.

(b) W/T Reception.

(1) 1 Telefunken H/F receiver, frequency range 1.5 to 25 mc/s. E 437 S.

(2) 1 Telefunken all-wave receiver, range 15 to 20,000 kc/s. E 381 S.

(3) 1 Telefunken broadcast receiver, covering usual broadcast short-long wave bands. Era 1012.

(4) 1 Radione broadcast receiver ditto. R2 or R3.

(5) The Radione receiver is used for recreational purposes, and programmes on it are played to the crew by means of 10 or so loudspeakers throughout the boat. The use of this set has been recently banned, as it is not proof against enemy D/F.

(6) Recently prisoners have mentioned a Lorenz H/F receiver called "Main", which has a frequency range of 3 to 20 mc/s. This receiver is said to be a superhet giving very good reception, and being proof against enemy D/F. This set replaces (b1) above.

(iii) Manufacturers.

Manufacturers of the above gear include (fact) Lorenz, Telefunken, Petersen, Radione, Kriegsmarine Werft (Kiel) and Philipps.

(iv) Arrangement of Sets.

(a) General. The position of boats communication equipment is much the same in all classes of boat. The majority of equipment goes into two cabins next to the control room. Cabin 1 is called the wireless room, and cabin 2 the hydrophone room, as it contains hydrophones as well as various pieces of W/T equipment. In 500-ton boats, cabin 1 has a floor area of 5' x 5', cabin 2 about 5' x 4'6". In larger boats a little more space is provided.

(b) Contents of Cabin 1.

(1) 150 Watt Telefunken M/F and 200 Watt Telefunken H/F transmitters.

(2) Telefunken H/F receiver.

(3) Sometimes Radione broadcast receiver.

(4) D/F receiver.

(5) S/T.

(6) G.S.R. receiver.

(c) Contents of Cabin 2.

(1) 40 Watt Lorenz H/F transmitter.

(2) Telefunken all-wave receiver.

(3) Telefunken broadcast receiver.

(4) Any "secret" experimental gear.

(d) Miscellaneous.

(1) VH/F transceiver in upper control room |

(2) Radar transmitter in Asdic shaft } when carried

(3) Radar receiver in control room |

(4) Radione broadcast receiver in Captain's cabin or Officers' quarters.

(e) Diagram

Port Side: Captain's and Officers' cabins. Starboard side: W/T and Hydrophone rooms.

Plan of Main Deck

(v) Operational Performance.

(a) H/F-W/T sets are primarily to enable U-boats to keep in touch with Control even when in distant waters. The Telefunken 200 Watt H/F transmitter, S 406 S, is normally used, the Lorenz 40 Watt being kept in reserve. The latter, with its higher frequency coverage, is sometimes more suitable.

Receivers Telefunken E 437 S of "Main", when fitted, are used for the reception of H/F transmissions from control. The Telefunken all-wave receiver E 381 S is available in case of breakdown. The above equipment appears adequate and maintenance presents no difficulty. (B2)

(b) VL/F. Enables U-boats to receive instructions and situation reports when proceeding at periscope depth through danger areas. For submerged reception the D/F loop and the VL/F band of the D/F receiver are used. For normal reception there may be between 5-10 ft. of water above the actual D/F loop. When "Goliath", a 1,000 kilowatt V/LF transmitter is operating, there may be between 15-20 ft. of water above the loop in both North and South Atlantic. (B2) The Germans attach great importance to VL/F.

(c) All important reports received by Control from U-boats and operational instructions from Admiral U-boats are sent out on both H/F and VL/F broadcasts (fact).

(vi) Intercommunication between U-boats.

(a) Direct intercommunication between U-boats is rare; U-boats listen out for H/F transmissions from other U-boats to Control. When, for instance, a pack of U-boats are operating against a convoy, co-operation between boats is ensured by making them keep watch on a convoy wave on their H/F receivers, and make their reports on the same wave. These reports are re-broadcast by control so that all boats will receive them, whether they have managed to intercept the originator's report or not. If one of the boats detailed for the task is unable to find the convoy, it will signal Control requesting M/F beacon signals from a shadower, and Control will detail a boat in contact to make the necessary signals. A similar is adopted if a boat is finding difficulty in making a rendezvous with a supply boat. (B2)

(b) Funkschlüsselgespräch. There is an authorised form of U-boat communication known as Funkschlüsselgespräch, consisting of direct inter-communication by W/T in cypher on H/F. Few U-boats have in practice used this type of communication. (B2)

(c) M/F Beacon Signals. The Telefunken M/F transmitter 2113 1 S has a range of 50-100 miles, and is only used in conjunction with one of the jumping wire aerials for making beacon signals. It is not very satisfactory (B2). Reception is by the D/F loop and M/F band of the Telefunken D/F receiver E 539 S.

(d) D/F. Telefunken D/F receiver covering two frequency bands 15 to 33 kc/s (VL/F) and 75-1,200 kc/s (H/F), type T31 Lä 38. In Autumn 1943 a D/F set has been fitted to some U-boats to enable them to take bearings on convoy R/T, covering at least the lower half of the H/F band (B2). Made by Lorenz. (C3)

(e) S/T. Most U-boats carry S/T consisting of a transmitter and receiver normally used during trials. It is easily detached and only rarely used operationally. It has a range of about 10 miles, working on a sonic frequency of about 3.5 kc/s. (B2)

35787 B 4

(f) VH/F. The VH/F set carried by U-Boats is a Lorenz 1 Watt transceiver type Lo 1 U.K. 35 with a frequency of 41.55-45.75 mc/s. The range is about 10 miles and the set is usually but not always removed after Baltic trials, before U-boats become operational. (B2)

(g) V.S. Owing to the removal of VH/F communication sets, short range signaling has to be by V/S. An Aldis type signaling lamp, Scheinwerfer E.S. W.20 is used. (C3)

(h) Infra-Red. It is possible that the Germans are fitting in U-Boats an infra-red signaling device known as Seehund, consisting of an infra-red signaling unit and suitable search glasses. These could be used for station keeping, signaling or recognition. (C2)

(vii) Aerials.

(a) W/T. (i) Jumping wire aerials are carried, one usually forward of the bridge for normal transmission of H/F and M/F, and one or two aft of the bridge to the stern. The forward aerial is about 15 yards, the after sections about 18 yards in 500-ton boats. By means of an aerial exchange any of the jumping wire aerials can be connected to any transmitter or receiver.

(ii) An extensible rod antenna for transmission and reception of H/F is also occasionally fitted. It is mounted on the port side of the bridge, and, when fully extended, stands about 20' above the conning tower (fact). No details are available as to its insulation. Its performance is poor, and, as a Radar mattress displaces it, its fitting may well be discontinued. (B2)

(b) D/F. A loop antenna is provided, about 2'6" in diameter, and about 2' clear of the bridge casing when fully extended. It is fitted on the starboard side of the bridge and is retractable under cover of the bridge casing. This aerial is used, in conjunction with the D/F receiver, for bearing indication on M/F, and for reception of VL/F. (Fact)

(c) VH/F. A rod antenna is used, about 4' high, on the port side of the conning tower. It is presumably dismantles, when the set is removed before operational patrol. (B2)

(viii) Manning.

A W/T complement of 2 P.O. Tels. and 2 Tels. is general throughout the U-Boat service.

The division into watches is three day watches, lasting four hours each from 0800 until 2000, and two night watches, lasting six hours each from 2000 until 0800, with one P.O. and one Tel. on together in each watch.

On the surface the U-Boat is watched continuously on the H/R receiver. The junior operator will usually help the senior in watching the set or in doing the cyphering.

In danger zones, such as the Bay of Biscay, or near a convoy, the G.S.R. (see Section IV) is manned continuously. Other ratings, usually S.T.s, are detailed from the crew to make up the G.S.R. complement, as they must relieve each other on the instrument every hour. If anything which may be enemy location is picked up, it is immediately brought to the attention of the P.O. Tel.

Additional burdens during convoy attacks are those of manning the M/F D/F to take bearings on beacon signals, and of manning the Radar set if required.

When submerged, watch is kept on the U-boat VL/F transmissions from Control by means of the D/F loop aerial and D/F receiver.

In addition, the P.O. Tel. of the watch is responsible for manning the hydrophones.

(ix) Interception of Allied Communications

The D/F set in some U-boats enables bearings on convoy R/T to be taken.

A few U-boats carry specialists carefully trained in the interception of Allied communications. This is an experimental procedure, not as yet widely used. (B3)

In this connection the following technical equipment has been mentioned:

(a) Telefunken R/T receiver: Covers a very wide frequency range in five bands (B3)

Band 5:	2 mc/s		Band 4:	2-6 mc/s		Band 3:	7-15 mc/s
Band 2:	14-24 mc/s		Band 1:	200 mc/s

(b) Lorenz D/F receiver, with frequency bands the same as for Telefunken R/T receiver, arranged in the same order. (Note: It is unlikely that bearings can be taken throughout the range).

Bearings are taken on convoy R/T, and convoy R/T traffic studied. The existence of "Hedgehog" was discovered by this means. Aircraft-ship R/T traffic is also watched, and prisoners claim that this enables then to estimate the number of aircraft associated with a convoy.

(x) Trend of Development.

There is little indication of any change in U-Boat W/T equipment.

The "Main" H/F receiver may be more widely fitted, as its performance is said to be very good.

The use of a D/F receiver capable of taking bearings on convoy R/T is likely to become general.

Increased interception activity is possible on the part of boats carrying specialist operators.

It is unlikely that VH/F will be reintroduced for convoy operations or that the use of S/T will be increased.