The Zenith of AA Machine Guns

The USSR began working on the issues of protecting armoured vehicles from air attack in the early 1930s. The first plans were to create specialized self propelled anti-aircraft guns, but work on these topics did not pan out. Instead, the Red Army received tanks with AA machine gun mounts. This mount was developed at experimental factory #185. It was accepted into service as the P-40 in 1935 and entered production a year later. M.A. Shufrin was the lead engineer on this project. Ironically, his initials were rarely seen in association with factory #185, even though this was one of the few products of factory #185 that truly saw widespread use. Mass production of the mount began in 1937. Variants were installed on the T-26, BT-7, T-28, and T-35. At its inception it was the best anti-aircraft gun mount in existence. It allowed the DT machine gun installed on it to rotate a full 360 degrees. The DT machine gun was equipped with AA sights.

The KV-1 was the only new generation Soviet tank equipped with an AA machine gun, although it was not used frequently.

An equivalent mount was supposed to be used on new generation Soviet tanks. The A-20 was supposed to be the first tank to get it, although for a number of reasons this never happened. New support tanks that were supposed to replace the T-26 also lost the turret. The P-40 was actually initially developed specifically for the T-26. The only design bureau to keep the machine gun mount was Kirov factory's SKB-2. A mount similar to the P-40 was installed on the turret hatch. The mount was removable, and so it is often not seen in photos. Nevertheless, the KV-1 had an AA machine gun from the very beginning. This was the USSR's only tank with an AA machine gun at the start of the Great Patriotic War.

P-40 machine gun mount on a T-26 tank. The AA sight is not installed.

The fact that all tanks aside from the KV-1 lost their AA machine guns came up in the summer of 1942. A German airplane carrying a report on front line trials of the Henschel Hs.129 ground attack aircraft was shot down on June 25th, 1942. The MK 101 30 mm autocannon made this aircraft a dangerous enemy for Soviet tanks. The report revealed that the Henschel Hs.129 will be armed with the superior MK 103 autocannon in the future. The translated report made its way to the GABTU on July 5th, 1942. The GABTU quickly reacted to this new threat. Work on the SU-31 SPAAG was already underway and the vehicle made its way to trials. AA tanks on the chassis of the T-60 and T-70 with various types of armament were also authorizes. Finally, Deputy Chief of the GABTU Major General I.A. Lebedev ordered comparative trials of AA machine gun mounts, both domestic ones and those used on American and British tanks.

AA machine gun mount on the KV-1 tank.

The NIBT Proving Grounds was tasked with study of these machine gun mounts. At the moment the proving grounds was in evacuation at Kazan, but it gradually returned to its old location. The first studies resumed here in the summer of 1942, including trials of experimental SPGs and mobility of foreign tanks. As a result, the proving grounds gathered an impressive collection of armoured vehicles, including one of the first Churchill III tanks that arrived via PQ-17. 

Browning M1919A4 machine gun on the Light Tank M3. The traverse range was limited.

The trials included two Soviet tanks (T-26 and KV-1), two American tanks (Medium Tank M3 and Light Tank M3), two British tanks (Matilda III and Churchill III) and a Universal Carrier Mk.I. Soviet machine gun mounts proved superior. The offered a full 360 degree traverse range. The mount rotated along with the hatch. The AA machine gun was also equipped with specialized sights. The maximum gun elevation was 90 degrees, while the maximum gun depression was -5 degrees. This allowed the machine gun to fire at ground targets.

The mount is folded for travel.

The machine gun mount on the Light Tank M3 was very different. After extending it, it could only be used within a 30-35 degree traverse range. The maximum elevation was 60 degrees, the maximum depression was -20 degrees. The weapon could only fire somewhere to the rear and up if the gunner was located inside the tank. This was a fair assumption, as the machine gun mount on the Medium Tank M4 was clearly designed to be used without exiting the turret. This made the M3's machine gun mount quite difficult to use. In this case, it was better used from outside of the turret. Other American AA machine guns had a similar flaw.

AA gun cupola on the Medium Tank M3. The machine gun could only be aimed by watching the tracers.

The Medium Tank M3 machine gun cupola was special. It was also designed to be used without leaving the tank. The gun elevation ranged from +60 to -13 degrees. Not too bad, but there were caveats. For one, it was not very comfortable to shoot from this cupola, especially at some angles. Second, there were no sights at all. The gunner adjusted his fire according to the tracers, a common practice for American tanks. This made the effectiveness of fire quite low.

Lakeman Mounting on the Matilda III.

The AA mount used on British tanks was also quite interesting. It was known as the Lakeman Mounting in honour of its designer, British officer Thomas Lakeman. A Bren machine gun was suspended via a system of levers. A 100 round disk magazine could be used, but more often than not these guns used regular box magazines. This system had approximately the same characteristics as the P-40, although the depression was limited to -2-3 degrees. That is not too bad, considering that this was an AA gun.

The Churchill III had the best variant of the Lakeman Mounting, although disk magazines completely obscured the gun sight.

Different tanks had slightly different mountings. The Medium Tank Mk.II had its mounting attached to a hatch flap, Valentine tanks with two-man turrets had the mounting attached to the right side of the turret, which limited its traverse. Valentine tanks with rotating cupolas and Churchill tanks had their mountings fixed to the base of the cupola. This made usage more convenient, but there were still complaints that it was difficult to aim. It seemed that not only Soviet designers found issues with these mountings, since they later disappeared. One of the issues was that disk magazines completely covered up the gun sight. It was only possible to fire in a vague direction. There was also a machine gun mount for the Universal Carrier. It had full 360 degree traverse and good elevation angles. There was just one problem: this was the stock Bren tripod that had to be set up outside of the vehicle. You could theoretically hit an airplane with it, but not from inside the Carrier.

Bren gun mount carried in the Universal Carrier. It could be used to fire at aircraft, just not from inside the vehicle.

The results of these trials were quite interesting. On one hand, Soviet mounts were clearly superior. On the other hand, by the time the trials were held production of the KV-1 had ended. The KV-1S did not have an AA machine gun mount. The study of AA gun mountings was rather theoretical. Another burst of activity on this topic followed the Battle of Kursk, where German ground attack aircraft dealt palpable losses to our tanks. Designers remembered both SPAAGs and AA machine guns, but soon forgot them again. Production finally began after some motivation from above, but even then only for heavy tanks and SPGs. An AA machine gun mount was introduced on the SU-76M in the spring of 1945, but medium tanks had to wait until 1947 and the production of the T-54.

Original article by Yuri Pasholok.