There aren't any career/time leaps. If you start in 1941, you will literally go completely thru the war. I do think when you return to base, a couple weeks will pass before heading back out on another mission.
If you want to use some of the later boats and better equipment, start another career in 43 or 44 (if you want a Balao class sub). The game is coded where different equipment and boats become available to "buy" with your renown at a set dates. As far as new sub, I believe the game will award you one (you can't use your renown).
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