Conversation so far:
Where did Tom Lehrer go to school?
Lehrer earned his Bachelor of Arts in mathematics (magna cum laude) from Harvard University.
Did he go to graduate school?
1946.
He received his MA degree the next year.
Did Lehrer ever join the military?
He was drafted into the U.S.
Army from 1955 to 1957.
What was his rank in the military?
Lehrer served as an enlisted soldier, achieving the rank of Specialist Third Class.

Question: When did he finish his military career?
Self-contained rewrite: When did Tom Lehrer finish his military career?