What does SA stand for in the U.S. Navy?

Question

My uncle was part of the Navy and fought in the Vietnam War. On his grave it says "SA, US Navy, Vietnam". What does SA mean?

Answer 1

Seaman Apprentice which is E2 now.

Back then it would be very possible if he was not in the Navy for very long (ie got drafted).  

Answer 2

Seaman Apprentice, paygrade of E2.  

Answer 3

From the top of my head, the only SA I'm thinking of right now is Seaman Apprentice, an E-2.

Which would be extremely unlikely if your uncle was in the Navy for many years.