Complex sentence: In October 1937 he enlisted into Company "B", 1st Battalion, 102nd Engineer Regiment and by May 1940 was a corporal with the 102nd Engineers and promoted to supply sergeant.
Split into simpler sentences: In October 1937 he enlisted into Company "B", 1st Battalion, 102nd Engineer Regiment. By May 1940 he was a corporal with the 102nd Engineers and was promoted to supply sergeant.