I expect the US Army will demand a manual safety. Glock does have the capability to offer custom models with a manual safety to government agencies who insist upon it. It's a modification of the G18 machine pistol which doesn't share commonality in the frame and slide with the familiar G17 pistol. The geometry is completely different even though they appear the same when looking at them from arm's length.
My personal opinion is that if the military is restricted to using FMJ ball ammo, they should choose a cartridge with a projectile using the largest diameter and bullet weight. If that fails to meet their needs, then they should look at the smaller caliber high-speed armor piercing rounds like the FN 5.7 or Hk 4.6mm -- the former rather than the latter.
Wow, that was informative. I did not know Glock offered a manual safety.