[Fidd]

Ah well, that puts the tin-lid on it then. I had hoped that it had remained the case throughout the war, as it would have been useful in the larger multiplayer games to ID a particular boat by such registration letters. Oh well, back to the drawing board!

Edit: A universal light-signal for recognition would work:

U96 red white, red white, etc
H552 green white, green, white,
H564 green red, green red, green red
U307 white white (pause) white white

4 x greens - I'm watching you pass me
4 x reds - about to manoeuvre, watch out

EDIT As an alternative, perhaps a small pennant or life-bouy could be added in a different location for each boat, so the pennant, or position of the life-bouy or similar could be used to tell one u-boat from another?

etc