Ok first off, This may have been posted before but as I am not aware of it Im going to post it purely for your benefit So Please dont flame me saying this has already posted because I am posting it for you and you should be gratefull Im doing a favour.(My First Tutorial Btw )

Ok then guys lets get this started. First of all you need 2 spare classes to do this glitch. Atleast one should include OMA (One Man Army.) The Other Class Will Need A Riot Shield and anything else, I recommened the Riot Shield Class should have OMA aswell as another class just incase you get off the Turret you will need to do the glitch again.

Ok then so you need to go into a map which includes a Turret, also you need to have the Class with OMA on, while you are near the Turret you press Y (Xbox 360) or Triangle (PS3) and then switch to the riot shield class via OMA. While it gives you a notification "Changing Kit" While it is changing kit you have to Press X (for both PS3 and Xbox 360) on the turret, when you are on the turret wait for OMA to change and when the Changing kit notification is gone then on the bottom right hand corner of your screen you should see riot shield. If you see that then you have done the glitch correctly. You should now have a riot shield on while on the turret. I recommended OMA on your riot shield so if you accidently got off the turret you would have to do it again and change class by dying, that wouldnt be good if you were on a kill-streak.

+REP if i helped, thanks!