You can obtain a service record from the National Archives and Records Administration, 8th & Pennsylvania Ave, NW, Washington, DC 20408. 202-501-5400. You need one form NATF 80 for each person. They'll send it to you. You fill it out and send it back with check or credit card for $17.00 [last time I checked] and sit and wait for 90-120 days.
Service record is $35 but turn around is usually less than one week. Give Name as known, Rank, Unit and anything else you might think of.