I've been playing this game for years. I have made it to the end of the war once, but only by reloading my last save and keeping going.
I have tried perhaps 6 or so careers of "dead is dead", always starting in 1939. I have never made it to the end.
I'm currently in 1942 with a jam-up crew an a Type IXB, out of Lorient. I'm hoping to survive until the Type XXI at least!
Steve