Social Security offers an additional retirement benefit for those who were on active duty between January 1957 and December 2001. You paid Social Security on those earnings and therefore are entitled to benefits. Active duty includes active duty for training. Inactive duty training does not qualify.
If you served between 1957 and 1977 you are credited an additional $300 in earnings for each calendar quarter in which you received active duty pay. Service from 1978 to 2001 earns you a $100 credit towards earnings for every $300 you earned of active duty base pay, up to a maximum of $1200 per year. These credits don't translate dollar-for-dollar into your retirement benefit, but will increase what you receive.
If your active duty occurred between 1957 and 1967 the extra credits will be added to your record when you apply for benefits at retirement. However you must ask for the benefit – it isn't automatically applied. Bring your DD-214 with you to the Social Security office. If you served between 1968 and 2001 you don't need to do anything, the benefit is automatically added.