The army "learned" no such thing. There was never a safety problem with guns on military bases. Guns were banned by Bill Clinton as part of a broader gun control push by the Democrats.

The effect has been the opposite of increased safety. We've had a couple of unopposed mass murder incidents on US military bases since the ban went into effect, most notably by Nidal Hasan, who was able to kill 13 and wound 33 because nobody else had a weapon.