I've found useful in GWX the Enemies of Germany page, so I could easily determine if to sink a ship or not.
Now I've made a little mod to include a page in the help to aid us on our missions.
On a new help page all nations are listed which are at war with Germany in a timeline order with their map, so you can identify all enemy ships.
(Best use with OakGroove's SH! Flag replacement mod.)
Screenshot:
Download location:
http://files.filefront.com/Csengois+.../fileinfo.html
Feel free to use/modify my mod, just mention me in your credits.