The M9A1 was adopted by the US Army in the 1980s to replace the aging M1911A1 pistol. Its high capacity magazine and sturdy metal construction make it a reliable sidearm.
Compared to the M17 Modular Handgun System, the M9A1 carries 2 less rounds per magazine. All other operating aspects remain the same, like fire rate and damage.
The 652 rounds per minute is the maximum allowed rate of fire for the semi-automatic pistol.
The M9A1 is classified in-game as the Pistol. Pistols are backup weapons with low stopping power and minimal suppression effect. They have moderate sway, regular point fire responsiveness, and slightly more recoil than Carbines due to their unsupported nature. Changing stances have minimal impact on Pistol's recoil and sway.
Using Pistols as a primary is not a good idea due to the low damage and severe damage dropoff at range, as they don't necessarily have more controllability than Short Rifles. But it can save your life in a pinch when the enemy is caught reloading or when your primary weapon is out of ammo.
History
The M9A1 started out as the M9. It was in service to the US Army in 1990 to replace the Colt M1911A1 pistol. The M9 can survive harsh temperatures and is easy to use. The M9 incorporates many safeties, easily interchangeable parts, iron sights, a hard-chromed barrel bore, and an enlarged hammer pin. The M9 was updated in 2006 to a 1-slot Picatinny rail for attachments. The new updated version of the M9 is named the M9A1 and was adopted by the United States Marine Corps.
Trivia
The M9A1's appearance in Squad was inaccurate, as it was never adopted by the US Army but instead by the US Marine Corps. The Army continued to use the older M9 as the standard sidearm as of 2017 until it was replaced by the M17 MHS.