Damn, you’re right!
I found this on a USMC site:
“On 2 May 1967, Headquarters Marine Corps once again authorized two-year enlistments. To keep personnel turbulence to a minimum, the Commandant decreed that two-year contracts would constitute no more than 20 percent of all new enlistments. Between l July 1966 and 30 June
1967. Only 16.9 percent of all enlistments were for two years; over half were for four years.”
I was in the USAF (1970 - 1974), which was a four year enlistment. USN was a four year enlistment. USA was two years (if a draftee); three years if an enlistment. USMC was a three year enlistment, unless they grabbed you out of the draft (in which case it was a two year active-duty commitment).
Anyway, a long time ago.