Saturday, 4 January 2020

From Sky to Earth

The concept of an airborne tank appeared in the early 1930s. The creator of this concept was John Walter Christie, who presented a tank that was supposed to get to the battlefield over the air using a discarding airplane attachment. Thanks to a powerful engine and a linkage to the propeller, the tank would not need an aircraft to tow it. This tank, known as the Convertible Airborne Tank M1932, never took flight, but the idea made its way into several countries. Christie himself quickly understood that a carrier airplane is necessary after all. There were two further developments: a plane that could carry a tank either underneath or inside it, or a specialized glider. Both developments were explored in the USSR and abroad. The Germans and British got the furthest with gliders, and the USSR, Germany, and USA got to practical stages with the aircraft approach. This article will discuss the fate of Soviet airborne tanks.

Under an airplane's wing

The fate of airborne tanks was fully linked to the success of airplane building. There were some issues with this abroad. Giant aircraft did exist, but they were very rare and had their quirks. The financial crisis that gripped the world in 1929 played a part. Christie's work slowed down for this reason. He continued to build airborne tanks with exceptional characteristics for their time, but they were not destined to fly. The reason for this was simple: there was no airplane to carry them.

Advertisements for the Christie M1933 Airborne Combat Car and its successors showed the tank carried by the Boeing B-9, but this was a delusion, as even the Christie M1933 Airborne Combat Car was more than three times as heavy as the airplane's maximum load. An unnamed Sikorsky aircraft was also mentioned in the data sheet, but this was also an attempt to pass off wishes as reality. The Americans had no airplane capable of lifting even Christie's 4 ton tank until the end of the 1930s. The situation in other countries was no better.

Christie M1933 Airborne Combat Car shown under a "Sikorsky airplane". This was only a commercial trick.

As strange as it sounds, the nation that had the best results in developing heavy bombers was the one that until recently lay in ruins: the USSR. Soviet aircraft development caught up with foreign powers and then took the first place. One of the symbols of the success of Soviet aviation was the TB-3 heavy bomber, whose prototype (ANT-6) rook off in 1930. The USSR made full use of German developments that had to work semi-legally due to the Treaty of Versailles. In designing the ANT-6, Tupolev borrowed the best ideas of Junkers designs. Four M-17 engines, licensed copies of German BMW-VI, were used. Later, in 1934, an improved version of the TB-3 was built that used AM-34 engines.

Thanks to new engines the bomb load increased to 3 tons. This was about the mass of the lightest Soviet tank, the T-37. The idea of the TB-3 as a tank carrier was tempting, especially since the USSR was interested in airborne tanks. The M1932 Airborne Tank was purchased, but quickly found disappointing. A new direction was chosen: development of a system that could transport mass produced vehicles over the air that could cover Soviet airborne forces with their armour and weapons.

Hooking up a T-37A amphibious reconnaissance tank underneath a TB-3 M-17 using Grokhovskiy's PG-12 system, 1935.

The first developments regarding carrying armoured vehicles by air began in 1932. The first stage was using a TB-1 bomber to transport T-27 tankettes. Large scale work began only in 1934. The first step forward was a development by the VVS Special Military Inventions Design Bureau (OsKonBuro). P.I. Grokhovskiy, its leader, was a leading specialist in the field of hitching systems. A design developed in 1935 and indexed PG-12 was universal. It allowed airplanes to carry cars and artillery, as well as tanks. Special mounts were installed on the tank, which attached it to the airplane.

Three TB-3s took flight in September of 1935 during the Large Kiev Exercises. They carried T-37A tanks, D-12 armoured cars, and trucks. The airplanes landed on specially prepared airstrips, the vehicles were unhooked, crews entered them, and they went into battle. The USSR became the first country to put the idea of the airborne tank into practice.

T-37A attached using the TVD-2 system under a TB-3 AM-34 bomber, October 1936.

The success was only partial in the eyes of the brass. The possibility of carrying a tank through the air was a success, but it had drawbacks. The biggest issue was that landing was necessary. This made the likelihood of losing the airplane much higher and made the deployment process more complicated. Ideally, a system was needed that could allow a tank to be deployed from a low height, as this would have made deployment simpler.

TB-3 en route to the drop zone, Medvezhyi lakes region.

The scientific research department of the VAMM began working on such a system. The Military Academy of Mechanization and Motorization was a veritable designer mill. Many designers who studied there went on to become famous. Two young specialists began working on the system dubbed TVD-2. The first of them was A.F. Kraftsev, the initiator of the project. The second was the chief of the design sector of the scientific research department, Military Engineer 3rd Class Zh.Ya. Kotin. The system was radically different from Grokovskiy's design. The attachments were not on the side, but on top of the hull roof, which made disengaging easier. Minimal changes were introduced into the tank and the airplane, which was a big advantage. The PG-12 required more substantial changes. In both cases, the tank was lifted up for attachment using pulleys.

The tank is deployed.

Work on the TVD-2 went quickly. Trials were performed in October of 1936. The tank was deployed into water from a height of 5-6 meters. The idea was that landing in water would be less stressful than on land, but that was not the case. Predicting that a water landing would not be soft, the designers developed three variants of protection for the floor. One was a wooden "boat" lined with sheet metal. The idea was that such a design, attached underneath, would protect the tank as it hits the water. The second idea was a steel sheet attached to the tank's floor. Pine branches were inserted between the floor and the added plate to cushion the blow. The final option was fixing tree branches under the tank.

The tank touches down. Theoretically, it was supposed to float, but it sank.

Three tanks were deployed during trials held at Medvezhyi lakes in October of 1936. On one hand, they showed that the TVD-2 system was a good design, as it performed flawlessly and the 3 extra tons of load did not affect the plane significantly. On the other hand, the landing was not very smooth. The floor of the T-37A tank was damaged in every case, and only the boat attachment helped it not sink. Other attempts ended in the same way: the tank's floor was damaged and it sank. The dropping process was also not easy. The crews had to be well trained to drop the tank from a small height.

The results of one landing. As a rule, this is what happened to the T-37A when it hit the water.

It is largely considered that work on dropping a tank from an airplane was concluded in the fall of 1936, but that is not so. Even Kotin's group continued working until the end of 1937. Work on systems that might cushion the blow when landing in water continued. Additionally, KB #29 began working on an analogous system in 1937. V.S. Vakhminstrov already had a lot of experience with designing systems that were described as "Vakhmistrov's circus". This system permitted the TB-3 to be used as an aircraft carrier. The design turned out quite good, but it was not accepted into service.

A variant of attaching the T-38 developed by KB #29. The tank's hull had to be drilled through for installation.

Vakhminstrov's design was similar to the PG-12. Four attachment points were installed on the tank's hull (the T-38 was planned in this case). They were held on with bolts, so the armour had to be drilled. The ABTU gave its permission, with the note that the openings had to be watertight, as the tank was to retain its buoyancy. Work at the KB #29 on this project began in June of 1937. In November the chief of the ABTU division commander G.G. Bokis gave the order to cease this work at both the KB #29 and VAMM. The reason given was that amphibious tanks were unsuitable for dropping into water. Bokis proposed that the effort should be concentrated in other directions. The first was to transport tanks by landing at prepared airstrips, a return to the PG-12 concept. The second was the idea of transporting a load up to 4 tons by air and lowering it from a height of 6-10 meters on water or land with pulleys. On November 23rd, 1937, Bokis was arrested on espionage charges. On March 19th, 1938, he was executed.

However, this was not the end of the airborne tank concept. Experiments continued in 1939-40, and the hitch was finally accepted into service. In late 1940 the Podyemnik factory began to produce these systems, which were sent to airborne units. 130 units for TB-3 bombers were built by May of 1941. As for Kotin and Kravtsev, their paths diverged in 1937. Kotin became the chief designer of SKB-2. Kravtsev's success in tank building was not as great, but he still made a significant impact.

In different directions

Hitches for the T-37 and T-38 were not the end. The Red Army accepted the new T-40 amphibious tank into service on December 19th, 1939. This tank was better protected, had more powerful armament, and most importantly was heavier. As with the predecessors, the T-40 was to be issued to airborne units.11 T-40s were sent to the 205th Airborne Battalion (Borispol) in March of 1941. The question of air dropping these tanks was a pressing one. According to NKO decree #23ss issued on February 28th, 1941, the People's Commissariat of Heavy Machinebuilding was supposed to develop 12 hitches for the TB-7 (Pe-8) heavy bomber with a 4.5 ton capacity for carrying T-40 tanks. 20 hitches capable of carrying a 3.5 ton weight were to be built in 1941 as well. The plans for T-40 hitches were significant: 200 were to be built in all. These requirements were never met.

The GABTU chief, Lieutenant General Ya.N. Fedorenko, sent a letter asking about delays to Zhukov on May 12th, 1941. An investigation gave a simple answer: there were not enough airplanes to satisfy the demands of airborne units. The last TB-3 was built in 1938 and the TB-7 was being put into production with great difficulty.

T-40 amphibious reconnaissance tank. It was supposed to replace the T-37A and T-38 in airborne units.

The airborne tank appeared once more in 1941, but the concept was different. This was no longer a tank-plane, but a tank-glider. For instance, aviation engineer A.Ya. Sherbakov developed a glider that could carry a NATI tankette. According to a letter to acting chief of the 11th Directorate of the People's Commissariat of Aircraft Production P.V. Tsybin, the glider would carry an 1850 kg load and be ready for trials by September. Sherbakov was not alone in his work. An analogous project was presented by TsAGI engineers R.S. Yermonskiy, A.I. Solovyev, and V.I. Matsyuk. This was a significant project with a 33.8 meter wingspan. The takeoff mass was 8 tons, 2 of which were made up by the glider. The tank was drawn very approximately. Its mass would be 6 tons, and the hull performed the role of a fuselage. The tail was attached to the hull.

The biggest requirement was the need to withstand a speed of 100 kph, as the glider took off at this speed. The tank also helped the towing aircraft by reaching this speed on its own power during takeoff. This project was met with disapproval from the GABTU, as no existing tank satisfied these requirements. However, this work came up many times later, especially since a tank glider did become a reality.

Yermonskiy's tank glider, June 1941. This and several similar gliders were rejected.

The T-60 overtook the role of a potential airborne tank by late 1941. The mass of the T-60 reached the same 6 tons that Yermonskiy counted on. However, TsAGI engineers did not take part in the new work. The topic of a tank glider was picked up in December of 1941 by the later famous aircraft designer O.K. Antonov, then the chief designer at the Glider Directorate of the People's Commissariat of Aircraft Production. One T-60 was provided by GAZ in late December of 1941.

Like a number of analogous projects, the glider (indexed KT, "Tank Wings", or A-40) was a removable attachment. The biplane glider was attached in four places to the tank. The driver, who also acted as the pilot, would disengage the tank with a special handle. Antonov planned that the KT would be made from non-deficit materials. The glider was supposed to be as cheap as possible, which was an important parameter for essentially a single use design. The overall mass of the glider and tank was 7.3 tons. The KT had a wingspan of 18 meters.

The KT (A-40) was supposed to look like this, although the real T-60 never flew with a turret.

An experimental prototype of the glider was built in April of 1942 in Tyumen, where the design bureau moved to after evacuation from Moscow. That summer, the tank and its glider were delivered to the VVS Scientific Research Institute in Zhukovskiy (Moscow oblast), where flying trials began. Judging by photographs, the tank's turret and armament were removed to save on weight. The KT was tested on land to ensure that the calculations were correct and the T-60's running gear could stand a speed of 100-115 kph. Three hover flights preceded the real flight. Since no TB-7 was available, a TB-3 with its engines supercharged to 970 hp was used. The airplane, flown by test pilot P.A. Yeremeyev, was also used in the summer trials of the KT glider. It was piloted by the famous test pilot S.N. Anokhin.

The KT before its first and last flight. 

The KT's first and last flight took place on September 2nd, 1942. After takeoff, it turned out that due to significant resistance the airplane could not accelerate past 130 kph, its maximum height was 40 meters. The TB-3 began to overheat and there was no other choice but to disengage the glider. The airplane headed for the nearby Bykovo airport, after which the glider disengaged. It's worth noting that Bykovo was not notified about the trials, so the appearance of a flying tank resulted in mixed reactions from the local AA crews. Anokhin masterfully landed the glider, after which he was promptly detained by airport security. After everything was cleared, Anokhin was released. The T-60 returned to the VVS NII without dropping the glider attachment on its own power. The fault in the failure of the trials was the KT design. In choosing a biplane layout, Antonov reduced the dimensions of the glider, but increased resistance. The glider had many struts and other elements that increased drag.

Further trials with a TB-7 (Pe-8) bomber were planned, but they never took place. The GABTU had a clear picture of what the T-60 was capable of and declined further work on a "winged T-60". However, the idea of airborne tanks lived. For instance, in April of 1943 a request came to the GBTU from N.A. Zhemchuzhin, deputy chief designer at factory #51. He was interested in the mass of new Soviet light tanks, as the idea of loading an airborne tank on a prospective airplane designed by factory #51 came up. The work did not progress past correspondence, and the BB airplane that was supposed to carry the tank remained in sketches.

The finale of Soviet airborne tanks was more the rule than the exception at that time. Analogous work in other countries met the same end. The only nations to use airborne tanks for their intended purpose were the British. However, the uses of the Tetrarch on June 6th, 1944, and Locust in March of 1945 were hardly successful. Airborne tanks were hopelessly obsolete on the battlefield, which the use of the Locust on March 24th, 1945, clearly showed. The only successful use of airplanes to transport tanks was the German use of Messerschmidt Me 323 Gigant transport aircraft to carry light tanks and SPGs. As for the USSR, the idea of building specialized combat vehicles for airborne units came up in late 1943. The first such vehicle, the OSU-76, appeared in 1944.

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