U-869 was known to the Admiralty/COMINCH tracking rooms by the bigram OI.  OI is mentioned in the following serial messages
Originator	Date	Date-Time-Group	Serial	Text
Admiralty	12 DEC 44	111931A	1435	3. OI EX KS 8TH DECEMBER TF AND TG AND TF DUE EX KS 10TH DECEMBER VK EX B 9TH DECEMBER RETURNING 12TH DECEMBER.
Admiralty	2 JAN 45	011850Z	1470	3.  BY 1729/29 OI TO STEER FOR CA 53.  BY 1654/30 OI TO REPORT POSITION.
Admiralty	22 JAN 45	212120Z	1427	2)  OI MOVEMENT PECULIAR BUT AM ASSUMING EN ROUTE GIBRALTAR IN VIEW OF 1743/19.  PLOT ON THIS ASSUMPTION WOULD PLACE OI NEAR CTG 22.8 ATTACK OF 16TH.  REQUEST YOUR VIEWS OF METHOD BY WHICH OI WAS ORDERED TO GIBRALTAR.  POSSIBLY MERELY ACTING ON SAILING ORDERS AND CONTROL MAY HAVE KNOWN OR ASSUMED THAT OI HAD MISSED ORDER TO GO TO CA.
COMINCH	22 JAN 45	222002	418	YOUR 1497 PARA 2 X SITUATION IS CERTAINLY CONFUSING X FROM ULTRA IT WOULD APPEAR THAT OBOE ITEM IS MOVING TOWARDS CA 53 WHICH IS SOMEWHAT STRENGTHENED BY WESTERLY POSIT OF 062347 AND FIX OF DF 090326 INDICATING POSSIBLE SW MOVEMENT X ON OTHER HAND A REPLY TO 191743 WOULD SEEM TO BE IN ORDER IF OBOE ITEM IS NOT HEADING FOR GIBRALTAR UNLESS HE SHIFTED TO SERIES 3 WITHOUT ORDERS AND MISSED THIS SIGNAL X WILL CONTINUE TO ASSUME OBOE ITEM ENROUTE CA 53 UNTIL SITUATION CLARIFIES
Admiralty	27 JAN 45	271715Z	1510	2.  COMMENT.  WE INTERCEPTED BERMUDA MESSAGE MENTIONED BUT HAVE NO OTHER DETAILS.  CAN YOU AMPLIFY.  DO YOU CONSIDER 1729/29 DECEMBER WAS REALLY INTENDED FOR OH NOT OI.
COMINCH	29 JAN 45	292010	421	CONSIDER THAT ERROR IN 291729 DEC WAS DUE TO ENCIPHERMENT SINCE SIGNAL WAS ADDRESSED TO NEUERBURG BY NAME AND COULD SCARCELY HAVE BEEN MEANT FOR KUHN WITHOUT EARLY DISCOVERY X NOTE THAT GARBLE OF ONLY ONE LETTER PRODUCES UNIQUE SOLUTION WHICH WOULD BE A LOGICAL HEADING FOR GIBRALTAR X IRRESPECTIVE OF FOREGOING CONSIDER SEA AREA HEADING FOR OBOE HOW PROBABLY IS CHARLIE ABLE
Admiralty	20 FEB 45	192035Z	1544	1.  BY 1059/19 VB AND OI AND NY TO AMERICA 0800/20 BY 1712/17 VB GIVEN 68 GROUPS OFFISIER NOT YET AVAILABLE.  QUERY VB PROCEEDING GIBRALTAR AFTER ALL.
COMINCH	20 FEB 45	202009Z	428	URSULA 091452 JAN ON SERIES 1 FURNISHES POSSIBLE CLUE TO OBOE ITEM MYSTERY AND SUGGESTS THAT MESSAGE WAS NEW OP AREA OFF GIBRALTAR X MY 418 REFERS X
COMINCH	12 MAR 45	122005Z	429	MY 428 X BY URSULA 091452 JAN OBOE ITEM ORDERED TO CHARLIE GEORGE 95
COMINCH	15 MAR 45	152006	430	AGENT REPORT 4 MARCH OF THE CAPTURE OF TWO U/BOATS OFF GIBRALTAR AND CONTRADICTING EARLIER SCUTTLING REPORTS MAY LEAD TO FURTHER STRENGTHENING OF CIPHERS PARTICULARLY WHEN REPORT IS APPARENTLY SUBSTANTIATED BY DISAPPEARANCE OF NAN YOKE AND POSSIBLY OBOE ITEM X ONE APPROACH MIGHT BE TO PERMIT NAN YOKE P/WS TO ASSOCIATE WITH A P/W WHO IS KNOWN TO USE CIPHER IN HIS CORRESPONDENCE X THIS WOULD ENSURE NECESSARY DETAILS OF SINKING GETTING BACK TO GERMANY WITHOUT AROUSING ENEMY'S SUSPICIONS (1) BY A PREMATURE RELEASE OF CORRESPONDENCE OF NAN YOKE P/WS AND (2) BY PASSING SUCH DETAILS IN PLAIN LANGUAGE WHICH NORMALLY WOULD BE CENSORED X TO COUNTER INFERENCE OF OBOE ITEM CAPTURE IN EVENT HE DOES NOT SHOW UP SUGGEST INTERROGATORS SUBTLY INFORM P/WS THAT HEIN WAS FIRST U/BOAT SUNK IN AREA FOR PAST NINE MONTHS X
Admiralty	18 MAR 45	172035Z	1584	YOUR 430.  HAVE ALREADY TAKEN STEPS TO MOLLIFY ENEMY APPREHENSION BY RELEASING NY SINKING TO RED CROSS ARRANGING FOR DATE TO BE DISCLOSED AS APPARENT SLIP AND FOR AGENTS IN GIBRALTAR AND SPAIN TO REPORT NATURE OF THE ENGAGEMENT WITH HMS RECRUIT.  OI PROBABLY BEST IGNORED FOR TIME BEING.  IN ANY CASE BP NOT ALARMED.