[mookiemookie]

Food aboard a U-boat was another interesting topic. At the beginning of a journey, as much food was cramped into every nook and cranny available in the U-boat. This resulted in one of the toilets being filled to capacity with food. They brought the best foods available with them, including fresh meat, sausages, bread loaves, fresh fruits and vegetables, but the small refrigerators meant that food spoilt quickly, especially in the damp environment of a U-boat. Very soon, fresh loaves of bread would sprout white fungi, which the crews promptly nicknamed as “Rabbits”, due to the white fuzzy appearance. By that time, food consisted mainly of canned goods supplemented by a soy based filler called Bratlingspulver. Issued by the military for U-boat crews, the crew unkindly referred to it as “diesel food”, due to the constant exposure of diesel exhaust that surrounded them.

http://www.uboataces.com/articles-life-uboat.shtml

You may also like this page, which lists the food carried on a IXC boat:

http://www.uboat.net/men/foodstuffs.htm