Meet the 2B1 'Oka': the Soviet Union's giant atomic mobile mortar

At the height of the Cold War, the Soviet Union developed an enormous tank-based, nuclear warhead-firing mobile mortar cannon.
Christopher McFadden
The 420-mm self-propelled mortar 2B1 "Oka" in Saint-Petersburg Artillery museum.
The 420-mm self-propelled mortar 2B1 "Oka" in Saint-Petersburg Artillery museum.

One half 3544/Wikimedia Commons 

  • In response to the U.S.' "Atomic Annie" gun, the Soviet Union felt they were falling behind technologically in the field of atomic-capable artillery.
  • So, they decided to make their own version.
  • This led to the development of the mighty 2B1 "Oka".

During the height of the Cold War, both sides of the "Iron Curtain" entered into a fierce "Arms Race" to attempt to get the edge on their enemies technologically. Most experiments were a complete failure, but, on occasion, some "out of the box" ideas paid off, albeit for a short period.

In what is possibly the world's strangest artillery piece ever conceived, you can thank this period for the birth of the enigmatic 2b1 "Oka". Let's check it out.

What was the 2B1 Oka?

The 21B "Oka," was a Soviet-designed mobile, large-caliber artillery piece designed to fire nuclear-tipped ammunition. Its creation was inspired by the initial tests of the M65 cannon (initially designated the T-131) dubbed "Atomic Annie."

The American weapon, designed for a similar role as the "Oka," was first fired in the spring of 1953 at a military training facility in Nevada. Like the "Oka," "Atomic Annie" was also designed to fire nuclear payload ordinance.

Meet the 2B1 'Oka': the Soviet Union's giant atomic mobile mortar
Frontal view of the 2B1 "Oka" with an example of its atomic shell in front.

As previously mentioned, the "Atomic Annie" test took place in May 1953 as part of the Operation Upshot-Knothole series of nuclear tests. The test was codenamed “Grable” as a phonetic stand-in for "G," as in "gun," since the warhead was a gun-type fission weapon.

The detonation of "Grable" occurred 19 seconds after its firing, with the round traveling around 8 miles (over 12 km) from the gun. The explosion was an airburst at around 524 feet (160 meters) above the ground, 87 feet (26 meters) west of its target, and 136 feet (41 meters) south of it.

Its yield was estimated at 15 kilotons, the same as the "Little Boy" atomic bomb. An uncommon feature of the blast was forming a precursor, a second shock front ahead of the incident wave.

For several years after that, work continued to refine the weapon and make it more reliable. The Soviets had nothing comparable throughout this period, making it a potential defensive weakness.

Something had to be done.

So, in response, the Soviet Union's Council of Ministers drafted a secret plan in November 1955 to develop their version. With this in hand, factories in various Soviet cities, namely Kolomna and Kirov, were requested to develop two new atomic munition delivery systems.

These were the "Condensator-2P" gun and the "Oka" 2B1 mortar, both types of a new kind of artillery. As you can appreciate, both weapons were developed in complete secrecy.

With regards to the "Oka," Soviet engineers were tasked with developing a mortar that could shoot a 1,653-pound (750-kilogram) nuclear projectile up to a range of 72 miles (45 kilometers).

The weapon would also need to be durable, reliable, and have a decent rate of fire. Mobility, among other things, was also deemed incredibly important for the final machines.

Meet the 2B1 'Oka': the Soviet Union's giant atomic mobile mortar
Rear view of the "Oka".

The Kirov Company, which had a lot of experience making specialized tracked equipment, was selected to start building the chassis. Rather than starting from scratch, the company decided to modify existing technology to get the job done.

Eventually, they settled on the most capable Soviet tank available at the time, the IS-5, to serve as the base for the planned 2B1 "Oka" mortar.

This chassis was widely available and came complete with a powerful 750-horsepower V-12-6B diesel engine. However, though powerful, the engine would only be able to muster a range of about 125 miles because of the weight of the intended 55-ton gun to be mounted to it.

Moreover, the chassis was intended to be typical for the "Condenser -2P" and the "Oka" mortars. This was for various reasons, but mainly because of the lack of alternative running gear and engines with sufficient power within the Soviet Union.

With the main chassis chosen, the next step was to figure out how to mount the monster 65.5 foot (20-meter) long 420mm gun to it. This was achieved, but there was still the problem of dealing with the gun's fearsome recoil.

While terrifying to see, there weren't many ways to handle the energy of the shot's "recoil" after it was fired. So, a kickback dampener was developed to handle the recoil integrated into the main chassis.

After development and testing, the 2B1 "Oka" mortar participated in a parade on Red Square in 1957, commemorating the anniversary of the October Revolution.

However, in the course of the actual tests, many systemic defects were identified. But these facts were not officially reported, naturally.

Four self-propelled 2B1 "Oka" mortars were assembled at the Kirov plant.

2b1 Oka vital statistics

Height: 9.8 feet (3 meters)

Weight: 61 tons

Entered service: Not applicable (never completed)

Manufacturer: Leningrad Kirov Plant LKZ

Main armament: 16.5-inch (420mm) main gun L/47,5 firing a nuclear-tipped shell

Powerplant: V12-6 700 hp diesel engine

Was the 2B1 "Oka" a failure?

In short, yes and no.

The engineers tasked with developing a Soviet variant of the American gun did achieve their mission. However, the weapon proved so impractical that it would ultimately prove to be a technological dead end.

The role it was intended to fill would also be filled with a different form of technology; missiles.

But, even in its day, it was seen as a vanity piece.

During a demonstration in Red Square, only one person, a driver mechanic, drove the mortar. The rest of the crew of six followed the vehicle in armored personnel carriers.

While its presence at the demonstration certainly caused a stir among the crowd, foreign journalists and analysts were less impressed with the centerpiece. Some even claimed that it was simply an attempt to intimidate the Soviet Union's enemies rather than being a genuine weapon of war.

In reality, the "Oka's'" detractors were on to something.

For example, the 420-mm "Oka" self-propelled mortar could fire successfully, but its design flaws made it entirely unrealistic for the actual field in combat.

To this end, three years after the demonstration in Red Square on the order of the Council of Ministers, the four prototypes of 2B1 "Oka" were effectively moth-balled from service.

Technical difficulties aside, tactical missile carriers had progressed in development and had excellent performance characteristics compared to weapons like the "Oka." The "Oka" was also considerably more expensive to build per unit.

The combination of these factors contributed to the “Oka” being eliminated as a practical weapon, and it would only go on to fill the ranks of military curiosities. Today, the only known remaining 2B1 mortar “Oka” can be in the artillery museum in the city of St. Petersburg.

And that strange Cold War hardware enthusiast is your lot for today.

Built-in response to the United States' work on "Atomic Annie," the 21b "Oka" was a fearsome machine. However, both weapons would ultimately prove to be a technological dead end. In the face of rocketry and rocket delivery platform developments, these weapons would never make it to the battlefield.

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