Since vitamin C cannot be stored in the body, first symptoms of scurvy (tingling in the gums) can begin to show witchin two weeks without any vitamin C intaque.
Sourkraut is a reasonable vitamin C provider, a reason why Dutch ships had no problem in reaching the East Indies with healthy crews and got ahead of the Brits.
Fresh cabbages last about a month, if stored properly.
Cabbage salad:
Chop cabbage real fine, season with lemon and salt.
Bratwurst, boiled potatoes and sourkraut will give you a typical U boat dinner.
Even in the dry US Navy, submarine captains carried 4-5 whiskey bottles for medicinal purposes.
My U-boat cocktail consists of Cuban rum, cream and a bit of sugar. After sinking a battleship, I add a farting banana.