Complex sentence: By the outbreak of WWII he was second-in-command of the newly built submarine "Trident", and by the spring of 1940 he was engaged in operations in the Norwegian Sea, as the Germans launched their occupation of Norway.
Split into simpler sentences: By the outbreak of WWII he was second-in-command of the submarine "Trident". By spring of 1940 he was engaged in operations in the Norwegian Sea, as the Germans launched their occupation of Norway.