The wake of the September 2013 fatal shooting of 12 people by a civilian military contractor who went on a rampage at Washington Navy Yard saw the recirculation of a rumor that gained currency after the November 2009 fatal shooting of 13 people by a U.S. Army psychiatrist at Fort Hood, Texas: that one of the reasons these mass shooters had not been stopped earlier in their killing sprees was because President Bill Clinton had issued an executive order back in 1993 that prohibited personnel on military bases from carrying firearms while on duty.
While there was at least a small kernel of real information underlying such claims, the gist of the rumor was wrong on two major counts.
It was during the presidency of George H.W. Bush, not Bill Clinton, that
the U.S. Department of Defense issued a directive in February 1992 affecting the carrying of firearms on bases by military personnel. That directive was eventually implemented through a regulation 190-14 issued by the Department of the Army (not via executive order) in March 1993, just two months after President Clinton assumed office.
Additionally, that change in regulations (which applied only to the Army, not other branches of the U.S. armed forces) did not ban the carrying of weapons by soldiers on Army bases; rather, it
restricted the authorization to carry firearms to personnel engaged in law enforcement and security duties, and to personnel stationed at facilities where there was "a reasonable expectation that life or Army assets would be jeopardized if firearms were not carried":
a. The authorization to carry firearms will be issued only to qualified personnel when there is a reasonable expectation that life or Department of the Army (DA) assets will be jeopardized if firearms are not carried. Evaluation of the necessity to carry a firearm will be made considering this expectation weighed against the possible consequences of accidental or indiscriminate use of firearms.
b. DA personnel regularly engaged in law enforcement or security duties will be armed.
c. DA personnel are authorized to carry firearms while engaged in security duties, protecting personnel and vital Government assets, or guarding prisoners.
snopes.com Clinton Disarmed Soldiers on Military Bases