In the scene near the end of the episode where the A-10 Thunderbolts make a strafing run, you hear the one plane firing what sounds like a heavy machine gun. The A-10 does not have a machine gun, it has a Gatling cannon (GAU-8/A Avenger) and when fired sounds like a short buzz because it fires supersonic rounds at 4,200 rounds per minute.
A dishonorable discharge from the military disqualifies an individual from police/detective service. Dr. McKay (David Hewlett) reveals the fact that Detective Sheppard (Joe Flannigan) was dishonorably discharged after a botched attempt at rescuing a medic from behind enemy lines in Afghanistan. However, he also stated that the record was expunged for political reasons.