Complex sentence: After its first war patrol, it put in at Wilhelmshaven probably sometime in April 1941 where it was given the coating, it covered the conning tower and sides of the U-boat, but not to the deck.
Split into simpler sentences: After its first war patrol, it put in at Wilhelmshaven probably sometime in April 1941 where it was given the coating. The coating covered the conning tower and sides of the U-boat, but not to the deck.