Conversation so far:
When did Ziaur Rahman begin his military career?
Ziaur Rahman began his military career upon graduating from the Pakistan Military Academy on 18 September 1955.
What was Ziaur Rahman's first position in the military?
Rahman was commissioned as a second lieutenant in the Pakistan Army.
Did Ziaur Rahman get promotions while in the military?
Ziaur Rahman was promoted to major.

Question: How long was he in the military for?
Self-contained rewrite: How long was Ziaur Rahman in the military for?