Ayoob; US armed forces....
Gun writer & tactics instructor; Massad Ayoob wrote in a recent(2011/2012) article that US Army troops carry the M9 9mmNATO, safety on empty chamber with a 15rd M9 magazine.
He said the USAF Security Forces(what were SPs) do the same on most bases; empty chamber safety on loaded pistol magazine.
They may have "cruiser" ready Mossberg or 870 pump 12ga shotguns or M4 5.56mm rifles(loaded magazines; 30-40rds)
Note; in CONUS, the MPs(and I think the SFs or Navy SPs/shore patrol) no longer conduct LE operations(Law & Order). This new DA(Dept of the Army) memorandum came out in 2012.
General security & LE details are done by 083 police officers(federal employees) or private contract security(PSCs).
They are armed & trained but can not enforce the UCMJ(Uniform Code of Military Justice).
Overseas(USFK, Japan, Italy, Europe, Africa, etc) MPs & SFs still have LE powers.