Complex sentence: He remained as FdU West until autumn 1944, when the Allied liberation of France forced the Kriegsmarine to transfer the remaining boats of 2th and 7th U-boat flotillas to bases in Norway, Denmark, and northern Germany.
Split into simpler sentences: He remained as FdU West until autumn 1944, when the Allied liberation of France forced the Kriegsmarine to transfer the remaining boats of 2. U-flotillen to bases in Norway, Denmark, and northern Germany.