Complex sentence: From 1943-1946 he was employed by the Calco Chemical Company in New Jersey, after which he worked with computers as a civilian employee of the U.S. Department of Defense from 1948 until his retirement.
Split into simpler sentences: From 1943-1946 he was employed by the Calco Chemical Company in New Jersey. Professionally, Chauvenet worked with computers as a civilian employee of the U.S. Department of Defense from 1948 until his retirement.