Convey Direction Finding Procedure - Appendix C

Procedure “A”

The Senior Officer will be ordered to transmit on 385 Kc/s so that his ship can be homed onto.  The operating signal ZDA or X687 with the time, recoded, is to be used.  Example:

X687  -  385  -  1100

Call signs and dashes of five seconds are to be sent.

Procedure “B”

The aircraft will transmit on 385 or 3925 Kc/s, ordering the ship (e.g. BMJ) to set watch on the D/F frequency (385).  Example of message:

           

X687  -  385  -  1100  -  X515  -  BMJ  -  3925

The bearings by the escort (BMJ) of the aircraft (BMJW) will be passed to the aircraft on 3925 Kc/s unrecoded.  Example:

BMJW  V  BMJ  -  095  -  1103    (the operating signal X722 may be used)

D/F watch is to be maintained until contact is made, or in absence of contact for two hours from time ordered.  Aircraft will transmit at intervals of not less than five minutes.

Procedure “C”

Exactly the same as Procedure A with the aircraft transmitting.

Procedure “H”

The Senior Officer of the group requiring D/F to bring about a “meet” will transmit direct or through a shore station to the other escort.  The homing wave will be 3925.  The S.O. addressed will tranmit for three minutes.  Listening watch is to be maintained on the homing wave for a further 12 minutes.  This procedure to be repeated at each subsequent three hours.  The DF’ing group will adjust course to meet the transmitting group.  If unable, the DF’ing group will signal on the homing wave a course for the other group to steer.

U-boat MF DF’ing

On receipt of a U-boat warning or of a close sighting report, at least one escort fitted with Medium Frequency Direction Finding equipment should be detailed to maintain D/F watch on the appropriate enemy homing frequency (384 or 437 Kc/s) for the next eight hours.  MF DF guards and special search ships will be detailed at convoy conferences, but watch will only be set by order of the Commodore when requested by the S.O. of the Escort.

DF’ing with Rescue Tugs

Escorts are to communicate on 2410 Kc/s or 500 Kc/s.  D/F bearings are to be requested and  passed using the “Q” code operating signals.