Hey, I found this in the Enigma General Procedure: "In the Fleet and Acknowledgment Procedures, addresses are to be put at the beginning of the message text and to be enciphered along with it." Since this is an acknowledgment, I did encrypt the adress (this is wierd, you need to dercypt all messages, just to find that most of them are not intended for you...must have misunderstood).
I have not changed the day key so people don't have to fiddle too much with the settings. Actually I find that changing all the settings at every message in a thread is tiresome and not really practical. I like it when people answer with the same settings as the opening message and maybe just change the indicator group.
I wouldn't change the key unless you decide to change the day. Otherwise all that is needed is a new set of indicator groups (message key) at the beginning and end.
Also, remember that YOU are out at sea are replying to the fleet, therefore encrypting is required. For you the U-boat, section 16 of the General Procedure applies, whereas the General Procedure applies to the initiator of the message thread. The only messages you are likely going to decrypt are those from BdU unless BdU instructs you to make radio contact with another boat. And BdU will list addressees.
Look in the DropBox and you will now find Marinefunknameliste_M.Dv.Nr.82-1.pdf. This will be the Radio Name List mentioned in section 15 of the General Procedure.
B123/AAA no stecker AAA ABC 1tle 1tle MHLS AYUW LFCE RQCY ESLI ERSD RDAL YCQY EJ