This weapon is a modified M1911A1 .45 caliber pistol sometimes referred to as "near match" or "combat accuratized." The MEU(SOC) Pistol is the designated "backup weapon" of Marines armed with the 9mm MP5-N Close Quarters Battle weapon. The M1911A1 was chosen for this role (and its modifications generated) because of its inherent reliability and lethality, and because the MEU(SOC) modifications make the M1911A1 design more "user friendly."
The unique characteristics of the MEU(SOC) pistol are: commercial/competition grade ambidextrous safety, precision barrel, precise trigger, and rubber coated grips, rounded hammer spur, high profile combat sights, and an extra-wide grip safety for increased comfort and controllability (which aids in a quick follow-up second shot). The issue magazines are replaced with stainless steel competition-grade magazines with rounded plastic follower and extended floor plate.

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Text coppied from www.defensedaily.com