The Thompson submachine gun: shooting a 20th century icon

Guns Magazine, Feb, 2008 by Mike Cumpston

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John Purcell shouldered the M1 Thompson and directed a series of short bursts at the steel gongs hanging 50 and 75 yards downrange. Each 10" rectangle gave forth a single resounding "clang" as the .45 ball rounds stitched a line through the dirt fore and aft. John bought the M1 Thompson from Interarmco in the late 1960s during his tenure as Sheriff's deputy. "It was a comfortable thing to have in some of the situations I got into with the Sheriff's Department and the Arkansas State Police, but I've mainly used it to entertain the kids."

John had announced he would be bringing the Thompson to the spring gathering of the Confederate Sixgunners of America convening in a remote hollow of the Arkansas Ozarks. Kids ranging in age from the single digit to creaky senescence created a mini-shortage of generic ball across the Southern States in cheerful anticipation of the event.

The M1 was the penultimate development of a saga begun in 1916 when General John T. Thompson founded the Auto Ordnance Corporation and began developmental work on a self-loading rifle based on a delayed blowback system patented by Naval Officer, John Blish. The Blish Lock never did work with the intermediate rifle cartridge envisioned by Thompson, but did function with the .45 ACP pistol round.

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Thompson coined the term "submachine gun" to describe what he believed would be a very effective weapon for trench warfare. The original "trench broom" was designed to fire from the hip, had two pistol grips, and no butt stock. It cycled at 1,500 round-per-minute and emptied a 50-round drum in about two seconds. This caused quite a sensation when he unveiled it at the Camp Perry matches of 1920. By then, of course, the War To End All Wars had ended.

Furthermore, alcoholic beverages had been eliminated by Constitutional amendment and the Volstead Act. One of the characters in Sinclair Lewis' novel, Main Street predicted a perfect Christian nation just as soon as cigarettes were abolished. Nevertheless, Auto Ordinance convinced Colt Patent Firearms to produce the Thompson Submachine Gun 1921A (15,000 units). While military contracts were limited, and sales were slow, the gun found favor with a number of police departments and was even marketed to civilians as a ranch defense weapon.

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The Model 1921 set the pattern for the Auto Ordinance Submachine guns of the 1920s and '30s, which came to include the Model 1927 semiautomatic carbine and the Navy Model of 1928. The standard model weighed 10 to 14 pounds depending on magazine type featuring a vertical fore grip, detachable stock, fluted, heat-dispersing, 10-1/2" barrel, and a fine Lyman aperture sight adjustable from 50 to 600 yards. Overall length was about 33". Rate of fire was a nominal 879 rpm. Magazine types include 20- and 30-round sticks and 50- and then 100-round drums.

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Basic fire controls include the selector switch located on the left side of the frame just above and behind the trigger and the safety lever immediately over the grip. On the pre-World War II models, the action knob is on top of the receiver. To prepare for firing, the shooter opens the bolt by way of the action knob, engages the safety with a rearward 180-degree rotation and inserts a magazine. Forward rotation sets the selector to full auto and the safety to the "fire" position. The trigger releases the bolt to travel forward firing the weapon. Experienced Thompson hands stress it is important to engage the safety before inserting a fresh magazine. This seems to relate to poor trigger control by some users but might also be a hedge against slam fires.

Early tests at the Colt factory established accuracy in semiauto fire at 1.89" mean radius (measured from center of group to outside edge) at 100 yards. Philip B. Sharpe fired a best group from the prone of about 2.5", center to center, at the same range. He had no trouble keeping deliberate semiauto fire inside of the kill zone of the Colt Police Target at 200 yards. The 10.5" barrel raised the velocity of the pistol cartridge from 810 to about 925 fps.

While Sharpe deemed the Thompson effective to "under 300 yards," the ball loads delivered lethal penetration at 500. Sharpe reported sustained full-auto bursts would quickly walk over the top of the target and recommended use of that mode of fire only for crowd control or engaging fleeing automobiles.

The basso-profundo leitmotif of the M1 echoed across the narrow valley for the better part of two days with no hint of stutter or stoppage. The entertainment value was high and the participants did not regret their purchases of loss-leader ball ammo. The M1, introduced in 1942 and replaced by the M1A1 a few months later, is a simplified version of the classic Chicago Typewriter of the 1920s and '30s. The optional Cutts Compensator muzzlebrake was gone as were the Blish lock and breech oiler. These items never were necessary with the .45 pistol round.

Simplified