The ‘Tommy gun’ was designed for soldiers. But Chicago gangsters made it notorious.

Except for Al Capone, Gen. John Thompson would be forgotten by all but serious devotees of military history. The two never met, being cut from different cloth.

Thompson, a khaki-clad military man who was awarded a medal “for exceptionally meritorious and conspicuous service as chief of the small arms division of the office of the chief of ordnance,” was the inventor of the Thompson submachine gun. A rapid-firing rifle, it was initially designed for trench warfare during World War I.

But a more storied use of the “Tommy gun,” as it was dubbed, was employed by minions of Capone, the nattily dressed king of the Chicago underworld in the 1920s and ’30s.

On Feb. 14,1929, gangsters burst into a meeting of mobsters in the garage of the SMC Cartage Company at 2122 N. Clark St. It was rented by George “Bugs” Moran, who used it as a distribution center for his bootleg liquor racket.

Seven men, members of Moran’s gang and hangers-on, were lined up against a wall and mowed down by submachine gun fire. Word on the street had it that Capone ordered the St. Valentine’s Day Massacre, as it has forever after been known.

Capone headed a rival gang and was in Florida on a vacation that seemed scheduled to give him an alibi. Moran was hiding. When he surfaced, he was asked about a rumor that the cops did it, since two of the four killers wore a police officer’s uniform.

“You must be new to this town, mister,” Moran reportedly replied. “Only Al Capone kills like that.”

His words were entered into the lexicon of Chicago legend and lore, as was Gen. Thompson’s deadly invention. Myriad moviegoers and television viewers have had a mental image of a Tommy gun when hearing the words. But few know the origin of the gun’s catchy nickname.

“To most U.S. cineaddicts the Thompson submachine gun is a gangster’s weapon,” Time magazine observed on June 26, 1939. “The late black-browed John Dillinger, potbellied ‘Killer’ Burke, the late Charlie Birger of Southern Illinois were virtuosos with the Thompson, called it, with utility in mind, a chopper.”

The gun’s alternate moniker was the “Chicago Typewriter” — the rapidly fired bullets echoing the click, clack of typing. The Thompson submachine gun was smaller and thus an easier to use version of a much larger machine gun in use at the time.  Two soldiers were needed to operate those older weapons. The gun was set up on a tripod. One soldier fired it, the other fed it belts of cartridges. It was a fearsome weapon when taking on an enemy force on an open battlefield.

But its weight and lack of mobility were a handicap when World War I’s fighting descended into the trenches of France. In Washington, the decision that the machine gun wouldn’t do was followed by arguments in Gen. Thompson’s office about what would. Some wanted to scale down the existing machine gun.

Thompson insisted that the design process should be reversed. What kind of weapon is needed? The obvious answer was: Something both mobile and able to fire bullets in rapid succession. The trick was to harness the power inherent in Sir Isaac Newton’s equation: For every motion, there is an equal and opposite motion.

A rifleman intuitively knows that. When he shoots a bullet, the rifle whacks him in the shoulder. Thompson designed a rifle where the kickback compresses the gasses the bullet left behind. The resulting explosion sends the next bullet flying.

A prototype was scheduled for field testing on Nov. 13, 1918. Two days earlier, World War I ended.

Thompson had returned to service after a civilian stint with a gun manufacturer, and had been the Army’s director of arsenals during the war. He retired for a second time and returned to work on his submachine gun, which he tried to sell to police departments and the FBI. But the cost of making them required price tags incompatible with a public agency’s budget.

However, Capone and rival Chicago mobsters dealt in products — booze and brothels — whose profitability made it good business sense to protect their investment with the purchase of Thompson’s gun.

As a result, the mobster rivalries in the bloody 1920s gang wars in Chicago was an uneven battle between mobsters armed with the Tommy gun and the public authorities not having them.

“Machine Guns Murder Novelty for Last Year,” the headline on a Jan. 1, 1927 Tribune story on the previous year’s murder rate read. The sub headline was: “Killings Fewer Here, But more Spectacular.”

The guns also became staples of Hollywood gangster movies. Included at one point in the vast arsenal held by Stembridge Gun Rentals, a shop on Paramount Pictures’ back lot, were 72 Tommy guns. The company’s logo was a musket barrel crossing that of a Tommy gun.

On the eve of World War II, it joined a hurry-up rearmament effort. Stembridge got a phone call from the Coast Guard when Japan attacked Pearl Harbor on Dec. 7, 1941. It was feared that California would be next, and the Coast Guard desperately needed small arms, including Tommy guns.

“We loaded them on trucks, and by night guns which had been used in gangster pictures were ready for the expected Japanese invasion,” recalled Fritz Dickie, Stembridge’s manager.

France and England ordered thousands of Tommy guns as World War II got underway. U.S. soldiers were also armed with the weapon. Bill Yenne’s 2009 book, “Tommy Gun: How General Thompson’s Submachine Gun Wrote History,” describes how, toward the end of the war, infantryman Mike Colalillo was sitting atop a Sherman tank during street fighting in Germany. “Here, take our Thompson,” a tanker said to Colarillo when his gun jammed, as related in Yenne’s book.

“He gave me some ammunition and said: “Be careful getting off the tank,” Colalillo later said in an interview.

Hearing faint moans of “Mike, Mike I’m hit”, Colalillo jumped off the tank, which withdrew. Colalillo carried the wounded soldier to safety across a battlefield the width of five football fields. He was awarded the Medal of Honor for “intrepidity and inspiring courage.”

Gen. Thompson never knew how his gun fared during the second world war. On June 22, 1940, the day France surrendered to the Nazis and more than a year before the U.S. entered the war, the Tribune ran a story datelined Great Neck, N.Y., that started this way.

“Gen John T. Thompson, U.S.A., retired, inventor of the Thompson submachine gun and in charge of design and manufacture of all small arms and cartridges for the government during the world war, died at his home today after an illness of three days. He was 80 years old.”

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