Unlockable costumes:
     Finish the following tasks to unlock the indicated costume:

In Campaign mode Kill 75 enemies       Unlock US Pilot outfit
In Campaign mode Kill 50 enemies       Unlock Navy Gunner outfit
In Campaign mode Kill 150 enemies      Unlock Secret Police outfit
In Campaign mode Kill 100 enemies      Unlock Special Forces outfit
Reach the "Specialist" rank            Unlock Kriegsmarine outfit
Reach the "Corporal" rank              Unlock Navy Crewman outfit