My son used the M-9 and a MK III Browning Hi-Power productively in Iraq. He said the nine kills pretty well if well placed, although he wished for JHP ammo.
He interacted with British SAS people, and they had pistols, usually H-K USP's, not a standard UK issue.
The pistol is not usually a primary weapon, except for couriers, MP's, and a few others. As an Air Force cop, I carried one with my nightstick. But if we expected a riot or were protecting a base in a combat zone, the AR-15 or a shotgun were issued, or an M-60 MG. The pistol then became a sidearm, used for emergencies.
On Guadalcanal, Marine Sgt. John Basilone, MH used his .45 a lot during a heavy Japanese attack. He managed to keep the four MG's under his command going, but used the .45 a lot, too.
Basilone received the Medal of Honor. He returned to combat and was later KIA.
Quite a few used pistols in most of our wars. You can see in old magazine photos that they were carried, and sometimes someone tells in his memoirs how he used one.
Patton, then a junior officer, killed several Mexicans with his fancy Colt .45 SAA in 1916, and British special ops people used them a lot in raids. I read a book where a South African officer in N. Africa in 1941 fired his .38 from his tank turret. During the Angolan war, a South African officer was in an armored car that ran dry of ammo for its main gun and the MG's. Cubans were swarming toward it, and the commander drew his Star 9mm and killed some. Shot them off the vehicle. Thankfully, he was soon rescued by advancing allied troops. He received the Honoris Crux/Cross of Honor for gallantry in that intense engagement.
Read, "Mosby's Memoirs" by Col. John S. Mosby, CSA to see how effective his Colt .44's were in the US Civil War. Some editions have pics of him wearing those guns. In close battle, he preferred the revolver to a carbine or saber.
His results suggest that he was right. He only named Colts. Some of his men may have had Remingtons or other brands. Most were captured from Yankees. He joked, "We didn't pay for them, but the US government did."
His 43rd Battalion of VA Partisan Rangers were among the most successful Confederate units of the war.
Winston Churchill wrote not only about his use of pistols in war, but told how his general, Sir Bindon Blood, drew his revolver and shot a Pathan tribesman who drew a knife on him at a peace conference. Sir Bindon was suspicious of the man, knowing their ways, but must have been a fast draw artist, maybe not wearing a conventional flap holster. Churchill didn't name his revolver. He (C.) wore first a Webley - Wilkinson M-1892 .455, then a Mauser C-96, and in 1915 bought a Colt Govt. Model .45 as he left for war in France. He still carried that .45 auto under his coat as Prime Minister in WWII. Its outline is quite obvious under a white suit jacket in a photo taken at Yalta or in the Med. theater.
