Prior to deployment, 2/4 CAV issued the M1911A1 in .45 ACP with Full Metal Jacket ball ammo.
The M1911A1 was replaced by the Beretta M9 (92FS civilian model) in 9MM Parabellum. The M9 replaced the M1911 series after 74 years of service in the US military.
Among the reasons for the switch was the high capacity, Double action, NATO caliber round and the age of the existing 1911's. The M9 beat out the Sig Sauer P226 for cost reasons.
The M9 is a short recoil, semi-automatic, single/double action, modified browning tilt barrel pistol that uses a 15-round staggered box magazine with a reversible magazine release button that can be positioned for either right- or left-handed shooters. The M9 was used with the Bianchi M12 Holster, though other holsters are often used.
The specific modifications made from the Beretta 92 includes:
Design of all the parts to make them 100% interchangeable to simplify maintenance for large government organizations.
Modified the front of the trigger guard so that one could use finger support for easier aiming.
Recurved the forward base of the grip to aid aiming.
Hard chromed the barrel bore to protect it from corrosion and to reduce wear.
New surface coating on the slide called Bruniton, which allegedly provides better corrosion resistance than the previous plain blued finish.
It also has an enlarged hammer pin that fits into a groove on the underside of the slide. The main purpose is to stop the slide from flying off the frame to the rear if it cracks. This was in response to reported defective slides during U.S. Military testing.
The M9 features multiple internal safeties, including a firing pin block that prevents the firing pin from moving without the trigger being pulled, and a firing pin striker that rotates when the safety lever is engaged preventing the firing pin from being hit even if the hammer falls. The M9 also has an ambidextrous external safety lever allowing both left and right handed people to engage or disengage the safety mechanism.
After having carried the M1911A1 for several years I absolutely hated the M9. I purchased the 92 FS when I left the Army out of nostalgia but after 6 months I sold it and bought my first Glock and shortly after, a 1911.
My daughter is a Combat Medic in the Army and although qualifying on the M9, she has been firing the 1911 since she was 8 and won't touch any other handgun.
In 2012, the Marine Corps issued the M45A1 (1911 platform) to MEUSOC manufactured by Kimber and later the M45A1 CQB by Colt.
The Beretta M9 is now being replaced by the Sig Sauer P320.