Roebling Alligator: Unexpected USMC Advantage

In 1933, engineer Donald Roebling wanted to find a way to save people stranded in disaster. After the 1926 Miami Hurricane and the 1928 Okeechobee Hurricane that resulted in thousands of deaths in South Florida, the need for a rescue vehicle was real. Roebling’s father suggested Donald build a machine to “bridge the gap where a boat was grounded and a car flooded out.” Unexpectedly, Donald Roebling’s philanthropic invention of the Alligator would eventually carry U.S. Marines to victory in the World War II Pacific campaign.

Fourth Division marines come ashore under fire on Namur Island, Kwajalein Atoll in February 1944. They are debarking from a LVT-2 amphibious tractor (AMTRAC). Image: U.S. Navy

It was fitting that Donald Roebling’s father used the term “bridge the gap” in his suggestion. Donald’s great-grandfather, John Augustus Roebling, designed New York’s Brooklyn Bridge, and his grandfather, Col. Washington Augustus Roebling, completed the plans and built it. Engineering was in the Roebling DNA. Donald would construct his part of the family legacy in Clearwater, Florida.

LVT AMTRACs loaded with Marines approach Iwo Jima 1945 Pacific War — Echelons of AMTRACs churn their way toward the invasion beach of Iwo Jima. LVTs evolved during the Pacific War, but all originated from the Roebling Alligator. Image: U.S. Coast Guard

Designing the AMTRAC

The Alligator was conceived as an amphibious tractor, or an AMTRAC, which could bring aid to victims on land or sea. Thought of by Roebling as a “Mercy Machine,” his tractor would plow through the most inhospitable swamp areas and then operate as a boat on the water with its tracks providing the propulsion. In a fortuitous twist of fate, the United States Marine Corps was at that time considering a vastly different application for an AMTRAC.

Donald Roebling began constructing prototypes for his Alligator and had a functional platform completed in 1935. Experimentation on the Alligator took place in Roebling’s personal workshop at his grand Spottis Woode estate on the Intracoastal Waterway in Clearwater. Components were also built in a secondary shop in the neighboring town of Belleair.

original AMTRAC Alligator in development — An original Roebling Alligator design undergoes testing in Florida.At this point in the development process, it does not yet look like the LVTs ultimately used by the U.S. Marines. Image: DoD

The initial challenge was the material used for the waterproof hull. Roebling settled on duralumin, an alloy of aluminum. It was lighter than steel, yet strong enough for the boxy structure. Duralumin was used for aviation in the 1920s and 1930s, notably for frames of airships such as the German Graf Zeppelin and Hindenburg, and the American USS Los Angeles, Akron, and Macon. Roebling had to explore methods for working with this new material for the Alligator.

Roebling Alligator testing in Dunedin Florida — Early testing of the Roebling Alligator in Dunedin, Florida. Developed for humanitarian rescue missions, the Alligator would go on to become a valuable wartime tool. Image: DoD

Roebling also struggled with his cleated tracks as they proved unreliable in hard use, but he was doggedly determined to build a vehicle that relied on the single-drive system to work on both land and water. His persistence was rewarded as he developed rugged, efficient tracks and obtained U.S. patent #2138207 for his system.

Marines and Coast Guardmen land in LVT-1 at Cape Cloucester 1943 — U.S. Marines and Coast Guardmen landing on Cape Gloucester, New Britain in December 1943. An LVT-1 leads the way as some men carry stretchers and others push a jeep toward the beach.

By 1937, the Alligator was in its fourth iteration. Model IV was approximately 20 feet long, 8,700 pounds, and could reach 18 mph on land and nearly 9 mph in the water. All prototype testing was done near Clearwater at the waterfront bluffs in Belleair, Honeymoon Island, and Dunedin.

LVT-1 AMTRACs on dock in New Zealand 1942 prepared for Guadalcanal campaign — U.S. Marine Corps LVT-1 amphibian tractors on the dock at Wellington, New Zealand awaiting embarcation on board ships of the Guadalcanal Campaign invasion force. Image: U.S. Navy

After concluding military operations in Haiti and Nicaragua in the mid-1930s, the U.S. Marine Corps was interested in developing a doctrine for fighting on amphibious terrain, especially for the transport of men and material from ship to shore. The Marines had tested a Christie amphibious light tank in 1924 but found it unsuitable for rough seas.

In the Spotlight

With Roebling rambling his rescue vehicles about in marshes, mangroves, and the beaches of Pinellas County, these activities drew the attention of the staff of Life Magazine. On October 4, 1937, Life ran a story about Roebling and his Alligator under the Science and Industry heading on page 94 of the issue. Included were photos of the AMTRAC being put through its paces.

USMC LVT-1 Bougainville invasion Campaign — A U.S.M.C. LVT-1 churns toward the shore during the Landings at Cape Torokina on the first day of the Bougainville Campaign in November 1943. Image: U.S. Navy

The Life article attracted the attention of U.S. Navy Rear Admiral Edward Kalbfus, who in turn, shared it with U.S. Marine Corps Major General Louis McCarty Little, who commanded the Fleet Marine Force. As the story goes, Gen. Little sent a copy of the article to the Commandant of the Marine Corps, Major General Thomas Holcomb. With a veritable ammo crate of brass enthused by the Alligator and its potential to solve the puzzle of amphibious landing, it was assured that Roebling would be consulted.

In February 1938, the Marine Corps sent a letter of interest to Roebling. He promptly responded, “The Alligator may be inspected, and we will be glad to demonstrate it to you at any time.” Mere weeks later, Marine personnel were scrutinizing the Alligator. The next two years would be marked by further examination and jumping through the many hoops of bureaucratic procurement procedures.

LVT-2 AMTRACs at Battle of Peleliu — First Division Marines head for the beach in LVT-2 AMTRACs during the Battle of Peleliu. Image: U.S. Navy

The Department of the Navy contracted with Roebling on February 22, 1940, to build 200 Alligators. The price would be 3.3 million dollars. With no way to manufacture the vehicles on such a scale at his estate, Roebling subcontracted with the Food Machinery Corporation (FMC) in Dunedin, Florida, just north of Clearwater, to build combat-ready steel Alligators. Later versions would be produced at plants in Lakeland, Florida; Riverside, California; and San Jose, California.

US Marines in LVT-4 head to beaches in Battle of Peleliu — Troop-laden LVT-4 amphibious tractors head for the the beaches during the invasion of Okinawa. In the background, the USS Tennessee (BB-43) fires her 5″ guns at the objective area. Image: U.S. Navy

Landing Vehicle Tracked in Combat

The first Alligators that were delivered to the Marines became known as the LVT-1, or Landing Vehicle, Tracked, Model 1. Roebling’s original Mercy Machine had proof of concept. The LVT-1 joined combat at the Battle of Guadalcanal in 1942. Many variations of the LVT would follow and serve with distinction during the war. Even the current Marine Corps AAV, Assault Amphibious Vehicle, is a descendant of Roebling’s original requirements.

Marines jump out of an LVT during the invasion of Guam in July 1944 — U.S. Marines clamber out of an LVT and take cover on the first day of the Battle of Guam in July 1944. Image: U.S. Navy

“There is not the slightest shadow of a doubt that the overwhelming victories of our forces at Tarawa, Kwajalein, Saipan, Tinian, Guam, Palau, and Iwo Jima would not have been possible without the AMTRACs,” said Vice Admiral E.L. Cochrane, WWII chief of the U.S. Navy Bureau of Ships. More than 18,000 LVTs would be built between 1941 and 1945.

Australian soldiers in LVT Roebling Alligator Battle of Balikpapan — Australian artillerymen in LVTs making for the beach during the Battle of Balikpapan in Indonesia. On shore, smoke from the naval bombardment of enemy positions is rising. Image: AWM

While the Dunedin FMC factory that built Alligators is now a parking structure, there is still pride in FMC’s contribution. The Veterans of Foreign Wars SPC Zachary L. Shannon Memorial Post 2550 in Dunedin has a refurbished LVT-4 on display. I took a quick drive over and was honored to have some vets take my photograph with Roebling’s innovation.

In Recognition

Roebling received a U.S. Navy Certificate of Achievement in recognition of the “exceptional accomplishment” of the Alligator. In 1948, he was awarded a Medal of Merit from President Harry Truman, “for exceptionally meritorious conduct in the performance of outstanding service to the United States.”

LVT-4 on display in Dunedin Florida — This LVT-4 is preserved at the Veterans of Foreign Wars SPC Zachary L. Shannon Memorial Post 2550 in Dunedin, Florida.

For a man with the vision of saving thousands of people from storms, Donald Roebling possibly saved millions with an invention that would move military might in both the Pacific and European Theaters and help the Allies win WWII. Roebling quietly resumed his amusements of mechanical tinkering, stamp collecting, and HAM radio in the post-war years. Roebling never accepted personal compensation for the Alligator and gifted the patent to his tracked system to the U.S. government. He passed away in 1950.

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