Saturday 25 January 2020

The Other Degtyaryev

The Red Army had two primary machine guns during the Great Patriotic War and the period preceding it: the light DP-27 and heavy Maxim. All Soviet armoured vehicles were equipped with a modified variant of the light machine gun. However, even these proven designs had their competitors. Given certain circumstances, they could have become widely used as well. One of them, the DS-39 heavy machine gun, even had a tank version produced and tested.

It was clear to the Red Army commanders by the end of the Russian Civil War that the Maxim heavy machine gun has a number of drawbacks and is not entirely satisfactory for the army's needs. The Germans arrived at a similar conclusion about their MG 08 a little earlier. As a result, the USSR adopted a family of machine guns designed by V.A. Degtyaryev: the DP-27 model 1927 light machine gun (Degtyaryev for Infantry) was followed by the DA (Degtyaryev for Aircraft) and DT-29 (Degtyaryev for Tanks) for installation into armoured vehicles.

A tank variant of the DS-39 with an extended stock (top) and attached bipod (bottom).

The creation of a tank machine gun that was satisfactory for the military dragged on. After many trials and improvements the "7.62 mm model 1939 heavy machine gun" or DS-39, a design by the very same Degtyaryev, was accepted into service on September 22nd, 1939. Mass production was set up at the Tula Arms Factory.

Production of the Maxim gun ended and the DS-39 was issued to troops. The reaction to real life use was mixed. Even though it was relatively simple and could be easily mastered by troops, complaints about frequent problems with the automatic mechanism began to come in. The most critical defect was separation of the round: the bullet was pulled out of the casing when the round was extracted from the belt.

Degtyaryev initially designed a new machine gun with a metallic belt similar to the high caliber DShK, but then it had to be converted to use a fabric belt. This resulted in serious changes and had an effect on the machine gun's characteristics.

The military insisted on using a fabric belt, as this way the ammunition supply was unified with the Maxim gun. Alas, the fabric belt was sensitive to moisture, which inevitably affected field performance, and the design of the loading mechanism was very complex. All of this led to malfunctions, especially for newer weapons. The VVS knew about this before the army, and aircraft guns tended to either use magazines or a more practical metal belt. However, the ground forces did not rush to convert to the more expensive metal belt. Not a single infantry machine gun with this type of feed was accepted until the middle of the Great Patriotic War. Mass modernization of Maxim guns to use the metal belt began only after the war.

In 1941 production of the DS-39 was ended and Maxim gun production had to be urgently restored. Various sources state that about 10,000 DS-39 guns were made. These guns were not removed from service and remained in use.

DS-39 tank machine gun configured to fight outside of the tank, three quarters view.

A report to the GAU (Main Artillery Directorate) chief, Colonel General of Artillery N.D. Yakovlev, stated that there were 1765 DS-39 machine guns still in service as of May 1st, 1943. Using higher quality ammunition from the ShKAS aircraft machine gun with double crimping of the casing increased the quality of service and reliability, solving the problem of bullets being pulled out or falling out.

DS-39 tank variant

The Automotive and Armour Directorate (ABTU, as of June 26th, 1940, the Main Automotive and Armour Directorate, GABTU) was looking for a replacement for the DT-29, for instance the ShKAS installed in a T-37A. One of the causes for this was the search for larger ammunition capacity, firepower, length of sustained firing. This could be achieved in various ways, including giving up magazine feeding in favour of a belt. The acceptance of the DS-39 into service did not bypass the tankers, who immediately attempted to adapt the new machine gun for tanks. This led to the tank variant of the DS-39, which in GAU and ABTU documents is named either the model 1939 or 1940 7.62 mm tank machine gun.

Tank variant of the DS-39 machine gun, stock folded in travel position.

The tank variant was developed at the Central Design Bureau #14 in Tula (TsKB-14). Development began in 1939 and ended a year later, leading to the difference in designation. The tank machine gun was altered to reflect the requirements for use in a tank.
  • The gas valve on the barrel was removed and replaced with a plug.
  • The rear handles and trigger lever were removed and replaced with a shoulder stock, pistol grip, and trigger.
  • The receiver was altered to be compatible with the new parts.
  • The machine gun was equipped with a bipod, similar to the one used on the DT-29, to be used outside of tanks. They were stored inside the tank separately. The bipod was installed using a clamp on the front part of the barrel. The top of the bipod had an infantry type open sight.
  • The muzzle attachment and and front sight were replaced with a flash suppressor.
The machine gun was tuned to fire at 850-900 RPM.

External view of the machine gun installed in a T-38 tank.

Two mounts were developed for the tank variant: one to replace the coaxial machine gun, one for installation in the turret of a light tank as the main gun. An AA mount for installation on the turret roof was also developed. All mounts were developed at the TsKB-14 in cooperation with Voroshilov factory #174.

The coaxial machine gun

Work on a coaxial machine gun mount was performed in parallel with the development of the tank variant of the DS-39 and was completed in January of 1940. The mount was installed in the T-26 tank, but the mount was universal and could be used on any tank in the Red Army.

The mount was installed in the gun mantlet of the tank along with a 45 mm gun. Fire was performed using a TOP sight or diopter sight at a range of up to 1000 m. The machine gun was fed with a belt of up to 250 rounds. Aiming was linked to the gun if the TOP sight was used, in this case the stock aiming mechanisms and pedal trigger were used, or separately. In that case, the gun was moved using the pistol grip and aimed through the diopter sight.

A coaxial gun mount developed by engineer Kurenkov.

The new machine gun was installed instead of the disk-fed DT-29. There were no changes to the zeroing process, as the relative position of the barrels of the main gun and machine gun, bore axis height, and other parameters remained the same. All vertical and horizontal aiming angles remained the same. The mount was composed of:
  • A split ball with a tray for attaching the gun.
  • A clip.
  • A clamp.
  • Two travel stops for the ball.
  • Two cones for attaching the gun.
  • The rear trunnion that was attached to the tray with bolts.
The magazine consisted of an ordinary ammunition belt box that fit a 250 round belt. The box was mounted on a carrier that was attached to the turret wall. New mounting points were not needed, the same ones that were used for the DT magazine rack were reused.

Variants of ammunition racks and belt feed on the T-26.

The machine gun had an associated rack, a row of boxes to store the magazines, toolkit, and bipod. The rack was developed specifically for the T-26 tank. The bipod was held in a sprung rack on the right side of the turret. Six magazines and the toolkit were stored in a rack on the right side of the hull, behind the driver. The front and rear left corners of the hull had racks for two magazines each. Two more racks were stored on the floor in the front left and right sections. The leftmost one was split into two sections, each of which had a separate locking lid that fit four magazines each. THe right one, closer to the driver, had two parts: lower and upper. The lower held various tools and parts for the tank. The upper had six magazines. The boxes were attached to the same mounting points as the old DT magazine racks. Overall the tank held 6250 rounds of ammunition. The old layout fit 47 disk magazines for a total of 3008 rounds.

Turret and hull machine guns

In addition to the coaxial machine gun, some Soviet tanks had a machine gun in a separate turret or in the hull. A special ball mount was developed for the DT for this purpose. A similar one was needed for the DT-29. It was ready by July of 1940.

The new mount combined an optical sight and the ball. If the optical sight was destroyed, a diopter sight similar to the one on the DT could be used. Trials were performed in the turret of the T-38 tank. The following characteristics were recorded: elevation from -15 to +20 degrees, horizontal range of 15 left and 15 right. The ammunition racks fit 3250 rounds, 1738 more than for the DT.

Engineer Polyubin's turret machine gun mount with an assembled ball.

No changes were required to install the new mount. The ball and racks could be installed in the tank as is. The only change was the position of the magazine in relation to the machine gun, which changed depending on what tank it was used in. The mount was composed of the following:
  • Ball mount.
  • Ball mount socket.
  • Brass catcher.
  • Sight forehead pad.
  • Two ammunition racks.
  • Magazine.
  • Diopter sight.
  • Rack for sights and spare barrels.
  • Belt guide.
  • Bipod rack.
  • Toolbox rack.
  • Porthole mantlet.
The ball mount was combined with the sight housing. It was installed in a socket connected to the tank's armour. A carrier for the machine gun, sight, belt guide, and brass catcher guide were attached from the inside. On the other side of the carrier a clamp and a mechanical sight checker were installed. The forehead pad was attached to the clamp.

Location of the machine gun mount in a T-38 tank turret.

An armoured mantlet protecting the most vulnerable parts of the machine gun mount was installed on the outside. There was also an armoured shutter for the sight opening. The shutter could be opened and closed from the inside with a lever.

The ammunition could be placed in two types of racks, one that went on the floor of the tank, the other that went on the side. The first was a frame that held 10 boxes of 250 rounds each, analogous to the ones used for the Maxim. The frame had separators and could be covered with a tarp. The second type consisted of racks where the boxes could be put and held down with a metallic belt.

Spare barrel and sight rack used on the T-38 tank.

The toolkit for the gun and optical sight was stored in a wooden box in a special slot on the side of the tank. There were also two bags for machine gun accessories. Spare barrels and sights were close to the gunner (to the lower right on the T-38) in a rack composed of a frame with four pairs of slots. The lower two held spare barrels, the one above them held a diopter sight, the top one held the optical sight.

The process of firing using the ball mount of the new tank machine gun did not differ from the process with the DT mount. The rules of firing were identical, except that the ejecting belt had to be guided downwards with the left hand so it did not bunch up.

AA mount

It was no less important to ensure that the new machine gun could be used in an AA role. The old DT could be installed on the P-40 mount, but the designers of the TsKB-14 designed a new AA gun mount that could be installed on a hatch. It was ready by June of 1940. It could be installed on the roof of a T-26 tank and fire at either airborne targets using a ring sight or at ground targets using a post sight.

Details of the AA variant of the machine gun in the position for firing at airborne targets.

The machine gun was fed from a box that held a 250 round belt, analogous to the one used for the Maxim gun. The gun was aimed by hand. A new hatch, 630 mm in diameter, had to be cut to accommodate the mount. Six 10.5 mm wide openings for the bolts had to be drilled and the yoke of the right ammunition rack had to be lowered by 7-8 mm.

The AA gun mount positioned to fire at ground targets.

The difference from the P-40 was that the machine gun was not stored on a pintle mount outside of the tank, but on the inner side of the hatch. When opened, the hatch flap served as both the mount and an armoured shield. The mount consisted of the following parts:
  • Circular rail guide on top of the turret.
  • Hatch flap.
  • Head.
  • Quadrant mechanism.

Materials that survive to this day lead to believe that the obvious routes of developing the DS-39 further would have been the introduction of a metal belt, conversion of the infantry variant to use the tank-style pistol grip and stock, and introduction of a bipod. This would have given the Red Army a universal machine gun, analogous to the MG-34. Alas, these proposals remained just proposals.

Finnish variant of the DS-39 ball mount.

Most of the DS-39 guns were lost in the first two years of the war, some of them were captured by the Germans and Finns. The latter used these guns in fortifications and developed their own ball mounts. The USSR also considered using the DS-39 to arm DOT-4 fortifications.

The tank variant of the DS-39 was never put into mass production, although it received the GAU index 56-P-423T. There is no evidence that mounts not mentioned in this article were ever developed, despite some blurry photographs of a knocked out BT tank.

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