Sunday 21 April 2024

Single Hatch for Tank Turrets

The interwar period was a time of new technical solutions, and tanks were no exception. Even though tank development was allocated a limited budget, experiments never stopped. The budgets began to swell in the early 1930s, which coincided with a rapid growth of tank characteristics. Various improvements were implemented, including those that improved the crew's working conditions. 

T-34 in Crimea, 1944. Factory #112 was the last to keep the turret with a single hatch in production. One of their tanks can be seen in the foreground.

One of the characteristic features of Soviet tanks and armoured cars in the late 1930s was the conical turret that came to replace the earlier cylindrical shape. Some vehicles also received a single hatch for their two-man turret. The T-34 tank was the most famous vehicle with this solution. This idea was dropped only to resurface in post-war designs. Let us discuss why this hatch appeared in the first place and why it disappeared.

A hatch and a shield

Initially, even two-man turrets had just one hatch. This layout was used on T-26 and BT tanks, and even on the three-man turrets of T-28 and T-35 tanks. The T-26 and BT soon got two hatches, but the T-28 and T-35 kept one for a very long time. This was not very convenient. At least a portion of these tanks were reworked during modernization. Two hatches were introduced, one of which was used for a P-40 AA machine gun mount. In the case of T-26 tanks and BT-5/BT-7 tanks, the split hatches were simply more convenient.

A typical Soviet two-man turret. There are two hatches. This was more convenient, plus it added the ability to install an AA machine gun.

A new chapter in the history of hatches began after the Spanish Civil War. Conical turrets are the best known outcome. The sloped sides of conical turrets improved protection. However, both the BT-7 conical turret introduced in the second half of 1937 and the T-26 turret introduced in 1938 had two hatches. Both of these turrets retained the ability to install a P-40 mount. The T-28 and T-35 main turrets also kept two hatches.

The BA-10 was the first Soviet AFV with a conical turret and a single hatch.

Armoured cars were the first to get a conical turret with just one hatch. A prototype of the BA-6M armoured car entered trials in the fall of 1936. It was later accepted into service as the BA-10. In order to reduce weight, the vehicle had a conical turret without a bustle. This made it less comfortable to work in. The space for hatches was also reduced. As a result, one large hatch was introduced. It also carried the ventilation cap.

T-35 turret with a single hatch.

A similar principle was followed when modernizing the turrets of the T-35 breakthrough tank. Its small turrets had no turret bustles since they would not be able to rotate otherwise. When modernizing the turrets, Kharkov had to follow the same path as Izhora. One hatch was introduced instead of two, although the ventilation cap was not moved to it.

The idea of a hatch-shield became popular in 1938. It can be seen on the T-116 project and on the A-20 and A-32 tanks.

What happened next with the single hatch idea is even more interesting. There were several prospective tanks developed in 1938. They included the BT-20 (A-20) and T-116 convertible drive tanks. The design explicitly stated that the single hatch was intended to protect the crew. The T-116 project also had a signal port in its hatch. It could also be used as a pistol port, although this was not explicitly stated.

The T-34 inherited the single hatch from the A-20.

The T-116 remained on paper, but the A-20 was built in metal and tested with its single hatch that doubled as a crew shield when opened. The same shield-hatch went on the A-32 and then on the A-34 (T-34). The idea of a shield-hatch that was born based on Spanish experience finally found its place.

The T-126 hatch was made with the same principle in mind.

The T-34 was not the only tank to have this feature. A similar hatch was used on the experimental T-126 support tank developed at factory #174. The draft project didn't say why such a hatch was found to be necessary. The final version also had a signal port that could double as a pistol port. Neither the hatch nor the T-126 went into production. The concept was reworked into the T-50, which had separate hatches and a commander's cupola.

Shield-hatch on the BA-11.

The last pre-war AFV to receive a shield-hatch was the BA-11. Unlike the BA-10, it had a signal port in the middle. The BA-11 went into production, albeit in small amounts.

Tempting idea and lacking implementation

The idea of a large turret hatch that could double as a crew shield was reasonable. It was very easy to get caught in small arms fire when evacuating from a tank. Nevertheless, the T-34 was the only tank to make use of this hatch, and even it finally lost it by 1943. The hexagonal turret already had two small hatches. What happened?

An attempt to save the P-40 mounting on the A-20.

For starters, the A-20's hatch already had drawbacks. As mentioned above, the T-28 and T-35 didn't get their dual hatches for no reason. They were needed to install the P-40 AA mounting. The P-40 could be installed on a single hatch, but it would be difficult. A mounting was designed for the A-20, but never built. As a result, the T-34 had no AA machine gun.

The T-34's hatch lid weighed about 100 kg.

That was not the worst of it. The A-20 and A-32 evolved into the T-34, which had thicker armour. The A-20's hatch lid was 10 mm thick, but the T-34's was 15 mm thick, plus it had additional equipment. As a result, the hatch lid weighed about 100 kg. There was a balancing mechanism, but it was still difficult to open. The hatch did more bad than good.

A turret with two more convenient hatches appeared by 1942.

The issue of the T-34's single hatch became apparent after the start of the Great Patriotic War. A wounded crewman was not always able to open it. The locks also didn't always work well and sometimes the tanks went into battle with the hatch open a crack. There was also no point in a shield-hatch, since evacuation hatches were installed in the floor of Soviet tanks back in 1938 (after experience fighting at Lake Hasan). They were not very easy to use, but it was better than catching a bullet. It's not surprising that the hexagonal turret that was developed in the fall of 1941 had two hatches. The design was taken from the T-34M tank that was never put into production.

A single hatch in the two-man turret of the T-70 tank. This idea was dropped on the later T-80.

The last instance of a single shield-hatch on a Soviet wartime tank took place in 1942. Modernizations of the T-70 tank resulted in a two-man turret that received a single hatch very similar to that of the T-126. Even the signal port was in the same place. However, the idea was quickly discarded. The tank needed better vision, but this was not possible to achieve with the existing design. The T-80 tank that grew out of the modernized T-70 already had a new turret with separate hatches.

Single hatch on the PT-76.

The two-man turret with one hatch found its place after the war. This type of turret was used on the light PT-76 tank. This was no longer a shield, however. The shape was made necessary by the round turret. The new hatch didn't have the weaknesses of its predecessors. For instance, a rotating commander's cupola was integrated into the hatch. The hatch weighs less and is easier to open.

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