Classic FBI Guns: Thompson Submachine Gun

At GunDigest, we independently review products. However, we may earn a commission when you purchase through links on our site. Learn More

Contrary to public opinion, the Thompson submachine gun was not only used by Prohibition-era gangsters. In fact, the “Tommy Gun” was a favorite among early FBI agents as well.

• The Thompson can be fired from 20-round box mags, or 50- and 100-round drum magazines.
• Rate of fire of the Tommy Gun is 1,500 rounds per minute.
• The Thompson was used in the FBI until the early 1970s.

The Thompson submachine gun was created by retired General John T. Thompson, who founded the Auto Ordnance Corporation to develop the design. The original gun had no stock or sights and fired at a rate of 1,500 rounds per minute. The design was modified and, in 1920, Auto Ordnance signed a contract with Colt Firearms to build 15,000, which were designated the Model 1921AC.

This model was equipped with a removable shoulder stock and an elaborate rear sight. It could be fired with 20-round box magazines or 50- (L) or 100- (C) drum magazines that required disassembly to load and featured a spring that had to be “wound up” like an alarm clock.

The military version had a horizontal forearm, but the FBI purchased theirs with a vertical foregrip. Most versions originally had a finned 10.5-inch barrel and a Cutts compensator to help control the recoil in full-auto mode.

The gun weighed about 10 pounds and with stock attached was just over 31 inches long. The design was based on a bronze lug that retarded unlocking the action, called the Blish Principle.

However, experiments years later showed that this didn’t have much effect and the weight of the bolt assembly controlled the pressure. The rate of fire of the Model 1921 was about 800 rounds per minute and this was thought to be too fast for military use. So most of the guns built by Colt were modified with a heavier bolt and stiffer recoil spring. This brought the rate of fire down to about 600 rounds per minute.

To identify these modified guns, the Model number was overstamped with number 8 over the last digit. These were then identified as Model 1928 Navy Model and often called “Overstamps.” This is the model most purchased by the Bureau. The gun was made in .45 ACP caliber. However, a few were made in a more powerful .45 Thompson caliber and even in .30 Carbine, but neither were used by the FBI.

The Thompson, also known as the Tommy Gun and the Chicago Typewriter, particularly in the press, was used extensively in the FBI until the late 1960s or early 1970s. When John Cox went through new agent training in 1961, his class shot Thompsons.

Back in the 1930s when the Thompsons were in heavy use, a carrying case was designed and built to FBI specifications. The black case, made by the Kansas City Trunk Company, held the gun with stock stored separately, a cleaning rod, and had room for four 20-round magazines and one 50-round drum mag.

They are now, of course, prime collector’s items, as is the spare parts kit in the shape of a 20-round magazine. During World War II, the Thompson was simplified to a straight, blowback design known as the M1. The bronze lug of the Blish system was dropped but the rear of the receiver had to be reinforced for reliability. The FBI never issued the newer M1 Thompsons.

Several courses were designed for the Thompsons. One was the “FBI Machine Gun Course.” (The Bureau continued to call them machine guns even though technically they were submachine guns, firing handgun rounds instead of rifle rounds.)

The course consisted of 50 rounds fired from 15 to 50 yards, both single fire and full-auto in bursts. The one-page sheet on the course erroneously called the magazines “clips.” The agents fired on a pair of Army E bobber targets, side by side.

Of course, the Bureau wasn’t the only agency that acquired Thompsons. Many police agencies, large and small, bought them. Unfortunately, this became a prime source of Tommy guns for gangsters. Many crooks, including Dillinger, stole them from police departments. (As were National Guard armories that were targeted for Browning Automatic Rifles.)

Around 1970 or ’71, FBIHQ ordered the destruction of most Thompson submachine guns in the field. The various field offices could keep a small number for tours and shooting demonstrations, and a few were kept at Quantico for use on the popular FBI tour in Washington, DC. In total there were 749 guns destroyed.

A few more were retained at Quantico. This destruction order was found to be premature, as there was no official replacement designated. The Bureau was then without operational submachine guns. The shortage caused a scramble for temporary replacements and several substitutes were acquired.

Lou Padula, the Principal Firearms Instructor at Washington Field Office, picked up many M3 and M3A1 “grease guns” from the military and many were retrofitted at the Quantico Gun Vault with thumb safeties. They were, of course, in .45 Auto but one arrived in 9mm Luger, probably a fugitive from British Lend Lease. The Gun Vault already had a grease gun in .45 caliber in its reference collection with a curved barrel for use by tankers. Several MAC 10s were also acquired.

Former Agent, Tom Riley, who also happened to be my firearms instructor, told me that he arranged with his contacts in the Marine Corps to obtain surplus firearms from the Navy depot at Crane, Indiana. He and other FTU instructors drove a Bureau car there, rented a trailer and hauled it back full of M3 “grease guns” and M1 Garands.

Later, he borrowed sample weapons from the Marines to evaluate for possible replacements for the Thompsons. They were particularly impressed with the H&K MP5 but FBIHQ didn’t want to purchase foreign weapons, at least at first.

The Bureau didn’t lack any spare parts for those Thompsons. Prior to their being phased out, the Academy Gun Vault received an interesting phone call from a supply unit of the U.S. Marine Corps. They asked if the FBI still used Thompsons and if the agency needed any spare parts, free of charge and transportation included. The Gun Vault replied yes and soon forgot about the offer.

Some months later, a phone call from Mainside, Quantico, advised the shipment of parts had arrived. Lester Limerick, then head gunsmith, told them he would have a pickup truck sent to the depot to pick them up. The reply: ‘Better send something bigger than a pickup. There are most of two boxcars full of parts for you!’

The Marine Corps had found a way to clear all its old inventory off the books with one call. The Gun Vault had to sort through thousands of parts, many still wrapped for long-term storage, to pull what they needed. A rumor is still going around that most of the parts were buried somewhere on the academy grounds. Indeed, the FBI could probably buy a new range complex for what those parts would be worth today.

The FBI finally adopted, in my opinion, what was at that time the finest submachine gun in the world, the Heckler & Koch MP5. We had already had experience with the short version of this gun, the Kurtz, and the SD, the suppressed model. The Bureau acquired the single-fire model, the SFA2, for field agents and the select-fire version for SWAT.

The gun was accurate, reliable and easy to fire. Its one drawback was that it didn’t lock back on the last round. To help overcome this, 9mm tracer ammunition was made available to some SWAT and HRT members who wished to add them to the bottom of their magazines as an advanced warning that they were about to go dry, a trick used by fighter pilots during WWII.

I recently discovered one of the most unusual Thompsons the FBI ever owned. Tracie Hill, President of the Thompson Submachine Gun Collectors Club told me about it and even sent me a photo. It was of a Thompson in 10mm! I couldn’t believe him. What on earth would the FBI want to convert one to that caliber? But my latest trip to Quantico confirmed that one was in inventory, assembled at the Academy Gun Vault, but no one still there could tell me why it was made.

When the Smith & Wesson Model 1076 was being adopted by the FBI, at least for a short time, it was decided to purchase MP5s in 10mm caliber. It took Heckler & Koch a lot of research and design work to make the conversion.

By the time they had the project completed, the 1076 was being dropped but they were so far along the FBI decided to still purchase the guns. It turned out that 10mm ammunition cost over twice as much as service 9mm but FTU thought it too late in the procurement process to change them to .40 S&W caliber, to match the new Glocks. There are still MP5s in the field, in both 9mm and 10mm, but they are seldom used.

Editor’s Note: This excerpt is from Guns of the FBI, A History of the Bureau’s Firearms and Training, available now at GunDigestStore.com.