Is there a chart of in-game German U-Boat types somewhere?
 

I just got offered a new submarine following a mission that ended March 1944. I decided to go for it but was shocked and appalled to discover that it had no Deck Gun. I'm NOT the best torpedo-man yet so I did a reload and turned it down.

Are there date ranges for given subs in-game and can I get some idea ahead of time whether I should jump at the next offer?

If you got a type XXI I wouldnt want a deck gun.

http://uboat.net/types/

I needed to ween myself from my over-reliance on deck gun so...
 

The boat was a XVIII, a Large combat version of a Walter boat. Lot fewer crew but a lot more fish, all inside.

I decided to recreate an alternate reality stream in which I took the XVIII
I'm just going back and starting the adventure but the thing can be a fuel pig!
Didn't understand the turbine controls on my first try and ran low on fuel less than half way to my destination am going back to refit and try again.

Thanks for the http://uboat.net/types/xviii.htm link though. I can use it to research any other boats I come across