[AS]

Unlike in the movie, the real Kaleun of U-96 survived the war. Buchheim merged 2 or 3 patrols into one to make his book more exciting and dense. The air attack happened, but it didn´t kill half the Crew and didn´t sink U-96 which was lost later in war.

If they want to milk the Das Boot cow, why not continue the original story?
Buchheim wrote about his adventures escape from Brest in his novel "Die Festung" (don´t know the English title, literally it is "The Fortress").