Complex sentence: During WWII he rejoined the military in 1940, inititally serving in the Royal Army Pay Corps as a Lieutenant, transferred to the General List in 1945, assisting the French underground, and left the Army as a Lieutenant-Colonel in 1946.
Split into simpler sentences: During WWII he rejoined the military in 1940, inititally serving in the Royal Army Pay Corps as a Lieutenant. He transferred to the General List in 1945, and left the Army as a Lieutenant-Colonel in 1946.