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Floating Tanks: The Ultimate Weapon of War?

Floating Tanks: The Ultimate Weapon of War?

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By Joseph Trevithick,War Is Boring

Amphibious assaults are the domain of the U.S. Marines, not the Army. But there was a period in history when the Army tried to out-do the Marines in hitting the beach—including planning how to deploy entire divisions of amphibious tanks.

Today, the whole concept seems more than a little bizarre. The Army isn’t much involved in amphibious warfare. But in the years after World War II, the ground combat branch had plenty of experience with seaborne assaults in the Pacific. Had Japan not surrendered, the United States planned to storm the home islands with hundreds of thousands of troops including more than a dozen Army divisions.

That influenced the fighting in the next war—Korea—as Army troops stormed ashore at Inchon. To many high-ranking officers it looked like “hitting the beach” would be a key Army job for decades to come.

“When World War II ended, the Army leadership believed their service should assume the amphibious warfare mission,” retired Army Col. Donald Boose, Jr. wrote in Over the Beach: U.S. Army Amphibious Operations in the Korean War. “But it was the Marine Corps that emerged from the defense unification and roles and missions struggles of the late 1940s with their amphibious warfare mission validated by Congress, the Secretary of Defense and the Joint Chiefs of Staff.”

But just in case, the Pentagon ordered the Army to be prepared—and to keep training—for amphibious warfare. This meant figuring out how to get the Army’s fearsome tanks off Navy transport ships and onto the sandy battlefields.

Then in 1952, the Army’s Armor School at Fort Knox, Kentucky published an entire study on how to use an armored division in an amphibious operation. “Armor has a place in an amphibious operation,” the officers wrote. “[But] the use of an armored division. . . is governed largely by the type and availability of the necessary equipment to get the armored vehicles. . . over the last three to six thousand yards of water from naval transports to the beach.”

One idea they proposed was divisions of floating tanks that could drive right up to the beach, fight alongside the infantry and quickly knock out any forts or other big targets.

It wasn’t a bad idea. . . in theory. The Marines today field armored, swimming troop-carrying vehicles for this purpose. Amphibious tanks had also been around for two decades by the time of the Armor School’s study. During World War II, every major combatant—except Italy—had produced some sort of floating armored vehicle.

The Soviet Union produced the first kind to go into mass production, the T-37, in 1932. Based on an experimental British design, the vehicle weighed just over three tons and had a single 7.62-millimeter machine gun. The Kremlin’s weaponeers eventually built improved designs using a different chassis. At six tons, the T-40 was the largest of these vehicles. But the Soviets pulled most of these types from front-line service early in the war.

In the Pacific, Japan had gone to war with a fleet of small and largely outdated tanks. Still, these types proved to be more than enough to help defeat Chinese and European colonial troops—at least in the beginning. In 1941, the Imperial Japanese Navy got its first Type 2 Ka-Mi amphibious tanks to help in capturing various island chains. Tokyo’s engineers created the vehicle by adding pontoons to the front and rear of a conventional Type 95 Ha-Go light tank.

Once on dry land, the crew could drop these floats and continue along their way. Twice as heavy as the T-40, the Ka-Mi had a 37-millimeter main gun and two 7.92-millimeter machine guns.

The Nazis planned to ride in submersible tanks during an invasion of the United Kingdom. Unlike other types, these vehicles would drive along the English Channel’s seabed at depths of nearly fifty feet deep using a snorkel to keep water out of the engine. They would then crawl out of the water and up the beaches toward their objectives.

It was not to be. When Hitler scuttled the proposed invasion and after brief service on the Eastern Front, the German army saw little need to keep working on these tauchpanzers.

The British and Americans came to the party relatively late. Unlike the floating Soviet tanks and the Japanese pontoons, British weaponeers chose a simpler means of getting tanks to ride on the water.

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In 1940, Hungarian-born engineer Nicholas Straussler cooked up a special flotation screen known as a Duplex Drive—or DD—to keep the water out. Before driving into the water, crews would deploy this canvas screen, effectively creating a buoyant hull. Propellers pushed the vehicle along. . . and when the vehicle hit land, the screen would drop back down, out of the way.

For four years, engineers tinkered with the concept on various older tanks. In the end, British, American and Canadian troops converted their famous M-4 Sherman tanks into “DDs” for the D-Day landings in Normandy and operations elsewhere in Europe. In March 1945, the floating tanks crossed the Rhine River as Allied forces pushed deeper into Germany.

The Fort Knox study considered the DD design as a possible option for the Army’s future Cold War force. The proven gear was easy to install, had little impact on the tank’s basic performance and didn’t add significantly to the vehicle’s overall size.

Existing landing craft and amphibious ships could basically carry as many DD tanks as regular tanks. And crews could raise and lower the screen at will to cross rivers, canals or other waterways farther inland after the initial landing.

Unfortunately, the screen was vulnerable to enemy fire, shrapnel and obstacles. Too many holes, and the vehicle would sink like a rock. In 1942, a prototype DD using a Valentine tank chassis sank after being peppered with machine gun fire in a test.

Still, there were few other options, and even those were worse. Before the American invasion of Okinawa in 1945, Army engineers had built a special pontoon boat hull—similar in concept to the Ka-Mi—dubbed the T-6. With this device, an M-4 tank could brave twelve-foot waves, according to the Fort Knox report.

More importantly, a tank equipped with the T-6 could fire its main gun at the enemy as it approached the beach, unlike the DD’s screen which blocked the crew from firing any of their weapons. The ground combat branch was happy enough with the equipment to formally add it to its arsenal and rename it the M-19.

However, the new-found stability came at a price. “Some of the disadvantages are readily apparent in the [T-6’s] specifications,” the officers at Fort Knox noted.

The kit more than doubled the length of the tank and added some two feet to the overall width. By itself, the gear weighed fifteen tons. “No improvement has been made in manner of propulsion and the speed remains about five miles per hour in water,” the Army reviewers added.

Even with the ability to fold the front and rear portions to save space, one of these floating vehicles would need as much room on a ship as three DD-equipped versions. A T-8 version for the M-26 heavy tank was even longer and wider.

Army engineers believed they could easily modify the arrangement to fit the newer M-46 and M-47 tanks. The Fort Knox officers also examined the Marines’ amphibious tracked vehicles, wheeled armored cars and “undersea” tanks like the German tauchpanzer.

“There is no indication of any development or research at present in the U.S. Army toward solving the problem of ship to shore movement of armored vehicles under their own power,” the Fort Knox team lamented. In the end, the group suggested that the most sensible option was to build better landing craft.

That settled the debate. Mostly.

The Army tried to hold on to its sea-going experience for several more years, but support within the service and the Pentagon was diminishing by the day. By the end of the 1950s, most Army amphibious units were relegated to hauling cargo or running small experiments.

In 1964, the U.S. Army Engineer School devised a massive amphibious training exercise dubbed Operation Sunset. Coming right before the American buildup in Vietnam, the scenario involved a massive seaborne invasion of Southeast Asia. “However, this immense and powerful organization. . . existed only on paper,” Boose explained.

In 1965, the Marines made an unopposed “administrative” landing at Da Nang in South Vietnam. The rest was history. Today, the Army’s waterborne troops and amphibious capability are relatively small and largely unknown—and there definitely aren’t any divisions of floating tanks.

Joseph Trevithickis a reporter for War is Boring, where thisarticlefirst appeared.

Image: Wikimedia Commons/U.S. Marine Corps.