The source: “Coming Full Circle: Replacing the 9mm with the .45 Caliber Pistol” by Maj. Craig R. Wonson, in Marine Corps Gazette, July ­2006.

In 1985, when the U.S. military changed its standard sidearm from the Colt .45 pistol to the Beretta M9 9mm, the decision seemed sound. The .45 had been in service since 1911, and though it was effective in battle, it was also much criticized: Its strong recoil made it difficult for inexperienced shooters to manage, it was too large for small hands, it was tricky to clean, and its single-action firing mechanism was a safety hazard. Not only was the M9 easier and safer to use, it also held twice as many rounds, and its 9mm ammunition was the same size as the standard NATO cartridge, as well as cheaper and ­lighter.

But according to Maj. Craig R. Wonson, future operations planner with the First Marine Expeditionary Force in Iraq, one crucial factor was overlooked in the selection of the 9mm pistol: the weapon’s ­effectiveness—­or lack ­thereof—­in “stopping” an enemy combatant. Now, with ­close-­quarter combat becoming “the norm” for American troops in Iraq and Afghanistan, Wonson says, the 9mm pistol has been seeing a lot of use, and it is not getting rave reviews. “Recent reports of the M9’s subpar performance . . . have left Marines with little confidence in the weapon,” he writes.

The shortcomings of the 9mm will not come as news to federal, state, and local law enforcement agencies. Many of them once used the 9mm but switched to larger-caliber sidearms, including the .45, after incidents such as a disastrous 1986 FBI shootout in Miami in which suspects suffered multiple gunshot wounds but were still able to kill two ­agents.

The problem is “stopping power”—the gun’s ability to take an opponent out of a fight immediately. Advocates of the 9mm argue that although it does not do as much damage as the .45, other ­factors—­such as the “neurological effect” of a bullet entering the body, the pain of a gunshot wound, and skillful shot ­placement—­should be sufficient to stop an enemy. Not so, says Wonson, especially if the enemy has taken drugs such as methamphetamines, as is reportedly the case sometimes in Iraq. And accurate shot placement is a risky thing to depend on in the ­less-­than-­ideal conditions of an actual ­fight.

Wonson advocates a return to a .45. Newer models by other manufacturers are easier to use than the old Colts, and just as effective. Indeed, the military had to learn this lesson once before: The switch to the .45 in 1911 came after smaller-caliber pistols failed to do the job in ­battle.