The original model sold to the US military was the 92F. Then there was some problems with the slides cracking. Supposedly, in at least one instance, the slide came off and hit the shooter in the face (supposedly a SEAL shooting very hot ammo).
Beretta changed the pistol slightly by adding a safety catch so that if the slide did break apart, the slide would stay on the frame. These pistols are the 92FS model.
Most people would agree that the 92F models are safe as long as you don't shoot a lot of hot ammo through them.
