Nazi Secret Weapon: The Krummlauf StG44

By Tom Laemlein
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Nazi Secret Weapon: The Krummlauf StG44

November 10th, 2020

7 minute read

As U.S. forces pushed deeper into Germany in the spring of 1945 near the close of World War II in Europe, more and more of the Nazi’s secret weapons plans were revealed. Some were nothing but rumors of advanced weapons technology, while others were impractical wastes of the Reich’s dwindling time and resources. But some represented remarkable advances in science, like the Arado 234 and Messerschmitt 262 jet aircraft, the V-2 (A4) missile, and the diesel-electric Type XXI U-boats.

U.S. Ordnance description of the German Sturmgewehr. Note the use of both the early (MP44) and later (Sturmgewehr) names for the weapon. Image: NARA

U.S. Ordnance “tech intel” teams traveled close to the advancing G.I.s, looking for examples of the latest German small arms. In the war’s closing days, they discovered a unique design intended to shoot at an angle, even up to 90 degrees.

U.S. Ordnance objected to the use of stamped parts and the “crude” fit and finish of the StG44, as well as the new intermediate 7.92 Kurz cartridge. Image: NARA

Throwing a Curve

U.S. troops found several examples of a radical firearms design called the “Krummlauf” (bent barrel) fitted to the new German assault rifle — the Sturmgewehr 44 (StG44). While most U.S. Ordnance reports of the era are highly critical of the StG44 (they greatly downgraded the design for its use of stamped parts, rough fit and finish, and particularly disliked its new intermediate cartridge), there was a great deal of American interest in the curious curved barrel attachment.

Here, a G.I. collects up German prisoners with an StG44 under his arm during the winter of 1944. Image: NARA

As for the numbers made, 500 units of the tank mount 90-degree “Versatz P” were reported made and delivered by Rheinmetall-Borsig. Approximately 1,500 sights for the tank device had reportedly been made by Zeiss by the end of January 1945. German plans were to equip every infantryman armed with the StG44 with the 30-degree variant of the Krummlauf.

The Sturmgewehr rifles quickly became prized battlefield pick-ups for many U.S. combat troops. Image: Author’s collection

Using the curved barrel, a German gunner would be at least 20cm below the edge of his foxhole or whatever cover he was using. The Krummlauf was certainly not a “war-winning” weapon, but its widespread use would have aided the German defense, cost more Allied lives, and lengthened the war.

The Krummlauf “bent barrel” attachment and sight for the StG44. Image: SANHS

I found some interesting U.S. Ordnance test reports of the Sturmgewehr equipped with the curved barrel extension, and this lets the men who examined the Krummlauf barrel extension speak for themselves. The following excerpts are from an Ordnance report on the weapon, which was carefully examined immediately after the war in Germany ended.

U.S. Ordnance demonstrating the Sturmgewehr rifle with the Krummlauf attachment. Germany, summer 1945. Image: NARA

U.S. Ordnance Report

Office of the Chief Ordnance Officer, July 18, 1945

The Krummmlauf reflector sight. Note the standard front sight reflected in the mirror. Image: NARA

General:

  1. The Krummlauf (bent barrel) is an entirely new idea in controlling and changing the direction of the delivery of a bullet. It consists of a bent barrel, cold-formed after rifling, attached to the muzzle of the machine pistol 44, now called the Sturmgewehr 44. It violates the old theory that a rifled barrel must be straight … .
  2. The Krummlauf opens up a new field of research. Its application to the Stu.G.44 has proven to be partially practical, permitting the gunner to fire around corners without exposing himself, deliver horizontal fire from a foxhole, or barricade, or cover blind while safely quartered within a tank. A reflecting type of optical sight permits the gunner to aim at his target, otherwise not visible to him.
  3. The data contained herein was obtained through interrogation of the inventor, Colonel Hans Schaede, assistant to Dr. Speer in the research division of Rheinmetall-Borsig by members of the Ord. Tech. Intel. Team #3; by test firing conducted by Capt P.B. Sharpe at Hq. Com Z, and by interrogation of German Major Fred Hartmann. Major Hartmann was formerly with the German Ministry of Armament, Division of Infantry Units, in Berlin, supervising research on small arms developments in Berlin, Kummersdorf, and the big proving ground at Hillerslaben.
The grenade launcher for the StG44 attached to the Krummlauf barrel with reflector sight attached. Image: NARA

Data and comments on the 30-degree barrel: According the inventor, the Krummlauf has an expected life of 6,000 rounds, but this is greatly doubted. Test firing indicates that the strain on the barrel in diverting the normal straight-line course of the barrel is great, and it is believed that it would enlarge, erode, and pocket, both in the auxiliary throat and in the curved area. All bullets test fired were seriously distorted, and this was verified by interrogation of Major Hartmann.

The 90-degree barrel extension shown attached to its hemispherical socket mount for use from within armored vehicles. Image: NARA

On test firing the 30-degree barrel, the “jump” or climb was greatly accelerated by the change in the direction of the bullet, but it was not too uncomfortable to shoot. The release of the gas through the auxiliary barrel ports relieved much of the apparent strain on the mechanism.

A tighter view of the hemispherical mount. Image: NARA

Data and comments on the 90-degree barrel: Although designed for tank use and fitted with a special interrupted screw thread adapter for quick detachment, the 90-degree barrel has also been found fitted to a standard clamp-on adapter. The model had been nicknamed “the around the corner gun” because it permits firing around a corner at right angles to the shooter.

The StG44 and the armored vehicle mount were predominately used on German assault guns and tank destroyers. Image: SANHS

It was anticipated that this weapon would be difficult to control, and test firing verified these estimates. As the bullet hits the curve in the barrel there is a violent reaction in the opposite direction. There is a combination of normal recoil, a tremendous torque as the rotating bullet undergoes the punishment of taking the new rifling with gas pressure relief, and a vicious sideways recoil. Approximately 150 rounds were fired in testing the weapon. Single shots and burst fire were tried, and, despite the attempts of several shooters to hold the weapon rigidly at the hip, more than three shots in automatic fire proved dangerous as shooter and weapon were spun almost 90 degrees. Firing tests into sawdust produced more fragments than intact bullets.

This Stug III has a curved shield for a remotely-fired MG 34 above the loader’s hatch — but the weapon could only be loaded when the gunner was topside. Image: NARA

Tank Mount: The mount is a hemispherical steel ball, assembled in a cup joint. The ball is pierced eccentrically to receive the barrel extension and pierced to receive a periscope sight. The weapon can be quickly detached from the barrel extension within the vehicle.

The 90-degree Krummlauf barrel modified for an infantry rifle. There was no sight available for this configuration. Image: NARA

Sight: Reportedly developed by Busch (at Rathenow), it is a 1.5x unit, with a 12-degree field of vision, mounted in the hemisphere to be coaxial with the sight axis of the gun. It appears that some 90-degree barrel extensions were modified for experimental infantry use in the last months of the war. The modification consisted of omitting the threading at the rear end of the barrel extension. The curved barrel is then pinned to a modified grenade launcher clamp coupling.

Bullets tended to fracture, shred, split, or otherwise deform in the Krummlauf. The arrow points to an unfired round for comparison. Image: NARA

Summary and Recommendations: Despite the fact that the bent-barrel theory is in violation of accepted ideas on bullet delivery, it is believed to be worthy of extensive research and development. With the short length, large diameter, and short bearing of the 230-grain U.S. Caliber .45 bullet, various degrees of bent barrels might prove to be successful, and with reasonable control. With the 7.9mm Kurzpatronen bullet, it is believed that the 30-degree bend is practical. The 90-degree bend is apparently impractical.—Colonel H.A. Quinn

American Anschluss

It seems that U.S. Ordnance took Colonel Quinn’s recommendation to heart. After the war, some curved barrels were created for the .45 caliber M3A1 (Grease Gun) submachine gun. Later, some commercial experiments were also conducted with curved barrels for the M1 Carbine (.30 Carbine). Apparently, the test results were not satisfactory. America, after victory in World War II, could not accept the middling results of a curved barrel project as Nazi Germany had been forced to do in her final days.

During 1947, a curved barrel unit was developed for the U.S. .45 caliber M3A1 submachine gun. Test results were apparently unsatisfactory and the project was abandoned. Image: SANHS

The curved barrel is an interesting idea, and U.S. Ordnance pursued it long enough to realize that the notion was more gimmickry than solid firearms science. Can a firearm be made to shoot around a corner? Ultimately the answer is yes, with the weighty qualification that the modification will not work particularly well or last very long. In the final equation, the Krummlauf and related projects weren’t practical. But, they certainly were interesting!

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Tom Laemlein

Tom Laemlein

Tom Laemlein is a historian. While that might sound mind-numbingly awful to some, he enjoys it. His deep dives into historical research keep him (mostly) out of trouble and, yet, too often away from the rifle range. Tom is the author of more than 30 books on military history and weapons systems. He regularly contributes articles to national magazines and websites on military history and firearms topics, and historical photos from his collection are used by publishers around the world. In those times that he is cornered in a corporate environment, he will talk about marketing until he is released. Tom is married to a very patient woman, and they live on America’s North Coast, near Lake Ontario. His regular misadventures with Wally, his young Tibetan Mastiff, remind him that life must be enjoyed full-bore, at least until you are ready for a nap.

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