Conversation so far:
Where did William F. Buckley Jr. go to school?
Alma mater. Yale University.
Where did William F. Buckley Jr. go to high school?
Millbrook School in Millbrook, New York
When did William F. Buckley Jr. join the military?
1944
How long did William F. Buckley Jr. serve in the military?
Years of service 1944–1946

Question: When did he join the CIA?
Self-contained rewrite: When did William F. Buckley Jr. join the CIA?