[Dietrich]

I assume by "single-mission", you mean one which is not part of a campaign - that is, a custom built mission provided with the game or one you have created yourself.

And by "patrol", you mean one that is part of the campaign itself.

What you need to do is install the emblem with the other SubEmblems. It needs to be a TGA file located in the data\Emblems\SubEmblems folder. I usually make mine 128x128 pixels, but I think 64x64 and 256x256 also work.

You then need to get that emblem onto your boat. This can be done by playing a real campaign for a few missions, and then getting the option (or alternatively, you can add the link in to your career folder by hand... which saves you having to actually play those missions).

Once done, this will give you the emblem, and it will appear on your U-boat in the campaign, single-player and multi-player missions.

Note however, that unless other players have that same emblem installed, only you will see it in any multi-player missions that you might play. (Other player's will not see it).