WELCOME TO SUBSIM!
(great, now I'm doing the sunny thing too)
well, Alex, there's not too many differences, and by all means guys if i'm wrong, please correct me.
there were 3 variants of the type VII, the VIIA, VIIB, and VIIC.
-the VIIA had a single rudder and an externally mounted torpedo tube, which was unreloadable until the U-boat reached port.
-The type VIIB had a re-loadable stern tube, and switched over to a twin rudder configuration.
-The Type VIIC was the final improvement that saw widespread use and is the most instantly recognizable of the three. The C variant had a slightly thicker pressure hull, allowing it to dive slightly deeper, but the thicker hull meant more weight, which slowed the boat down by abut a knot and a half.
the main differences you will find is in the towers.
-the normal tower had a single flak gun deck, on the A and B variants, the trailing edge sloped inward, on the C variant, it slopes outward.
-the second version had the single flak gun deck, but another flack gun deck was added on behind and lower than the original. this was considered a "quick fix" because of the short amount of time it takes to add on the new flak deck. allowing the U-boat to be in and out in a matter of days to a couple of weeks
-the third version had the same as the second, but the lower deck was larger to accomodate an even larger flak gun. these were usually 3.7 cm (as opposed to a single or double 20mm) or a 20mm flakvierling (that's 4 flak guns.)
-the last tower was only used on maybe 6 boats, this had the 3rd towers setup, but added another flak platform in front of the tower, making 3 flak guns for the ultimate in AA defense!
hope I was of some help!
