The U.S. Army is increasingly using civilian security personnel to guard its bases. There are now over 3,000 of these on duty, and the number is growing. Despite having 54,000 military police, increased security needs after September 11, 2001, and the demand for Military Police (MPs) overseas (where they guard prisoners, as well as provide base and convoy security), there have never been enough security personnel. Currently, 22 percent are overseas, and it used to be much higher when Iraq was still a major battle zone.
The U.S. Navy and Air Force also sent thousands of their security personnel to help out the army. The air force, in turn, faced its own shortages. In some cases, the shortage was addressed by transferring airmen from non-security jobs to the security forces. These airmen were given a six day crash course on basic security procedures, and then put to work temporarily (for one or more months), under the supervision of experienced security force airmen.
The 24,000 professional air force security personnel are also trained to use infantry weapons and tactics, in addition to their police and security training. But for guarding base entrances and high security facilities, six days will do it, and that frees up the professional security personnel to do the heavy lifting in combat zones.
For years ago, the navy faced its own growing security needs by expanding its own security forces. The navy has traditionally used marines for guarding sensitive locations. This included nuclear weapons storage sites, and key bases. But over the years, the marines have been, increasingly, replaced with specially trained sailors. Since September 11, 2001, that process has accelerated. And in the process, the navy has built a large security force.
The navy has never had a security force ( Military Police) like the army and air force do, so the navy has taken its existing security specialist, Master at Arms, and expanded it from, a few thousand, to over 10,000 personnel. These are now replacing marines in guarding key facilities. The marines will often still be there, but now the security detachments are typically be half marines, and half sailors (Masters at Arms). The marines are fine with this, given the manpower strains they are suffering because of the need to keep troops in Iraq and Afghanistan.