How can I verify if I was credited with my 4 years of service from July 1961 to July 1965 as a US Marine?

Hi,

Assuming you've already applied for benefits on your own record, you should have been asked to submit proof of your military service (e.g. form DD-214) when you filed, since military service credits weren't automatically credited until 1968. About the only way you could verify that you received the proper credits (https://www.ssa.gov/OP_Home/handbook/handbook.09/handbook-0953.html) at this point would be to contact Social Security and ask them to check to see if military service credits were included in computing your benefit rate. There should be an appropriate code on your benefit record that they can check for.

Best, Jerry