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Inventing the Amtrac

How Donald Roebling's "alligators," created to save lives, went to war

There is a quality that appears over and over again in American history. Genius and opportunity combine to create a pathway for transformation that changes the course of world history. In the U.S. Marine Corps (USMC), they called one such innovation the Landing Vehicle, Tracked (LVT), or amphibious tractor.

Amphibious tractors (amtracs) were a solution for a problem that did not exist in the minds of warfighters until the 20th century. Designed originally in the 1930s as a civilian rescue craft, amtracs became one of the key enabling technologies in the emerging doctrine of amphibious warfare in the 1940s. The amtrac story, however, is much more than just these facts alone. It is the story of a service’s transformation, one man’s humanitarian vision, and how they came together to help win a war.

 

Fertile Ground: Amphibious Development in the InterWar Period

The 1920s were both the best and worst of times for the USMC. Marines had won the first significant American victory of World War I at Belleau Wood, and had distinguished themselves in several other battles during the Allied offensive that defeated Imperial Germany, but suffered almost 12,000 casualties by the end of the war. In an American military that was rapidly being downsized, a few bloody victories on the way to Armistice Day were hardly enough to justify the continued existence of the USMC. What the Corps needed was a military specialty to call its own so that Marines would always be needed in the minds of American leaders. That specialty became amphibious warfare, and the USMC quickly committed to making it a new core mission.

“The development of the amphibian tractor, or LVT, which began in the middle 1930s, provided the solution and was one of the most important modern technical contributions to ship-to-shore operations. Without these landing vehicles, our amphibious offensive in the Pacific would have been impossible.” – Gen. Holland M. Smith, U.S. Marine Corps, 1949

What made such a shift possible were events that had taken place over the past quarter-century in the Far East and Pacific regions. Both the United States and Imperial Japan had acquired a number of new possessions from Spain, Imperial Russia, and Imperial Germany, following those countries’ losses in the Spanish-American and Russo-Japanese wars and World War I. Both America and Japan were beginning to look to who would dominate the Pacific and Far East in the 20th century. Inevitably, both the United States and Japan began to make plans for war against the other.

alligator

A later version of the Alligator mounting a bank as it emerges from the water. Developed to rescue hurricane victims and carry out other tasks in marshy terrain, the Alligator was a perfect solution to the needs of the Marine Corps. DOD photo

The U.S. document known as “War Plan Orange” was based upon the assumption that Japan would pre-emptively attack and occupy American possessions in the Pacific and Far East. The American Pacific Fleet would need time to gather and prepare, then move across the Pacific Basin to engage the Japanese. This strategy anticipated the taking of island bases along the way, which would require the use of amphibious forces and tactics that did not exist in the 1920s.

It is one thing for a military service to declare a new job specialty, but another to make it a viable profession. The Marines knew this and quickly put some of their most brilliant minds to making amphibious warfare a practical reality. One of these was the eccentric Lt. Col. Earl Hancock Ellis, USMC, known as “Pete” around the Corps. An early advocate of amphibious warfare doctrine, Ellis was the primary author of “Operations Plan 712: Advanced Base Operations in Micronesia,” which became the USMC’s bible for the planned assaults on Japanese-held islands that would be required to implement War Plan Orange.

However, even a quick read of “Operations Plan 712” shows that Ellis and the other USMC planners saw significant problems in assaulting the wide variety of islands in the Pacific. There would be a need for specialized equipment to allow Marines to get ashore to capture enemy territory and facilities.

 

Roebling’s Alligator

While the Marine Corps was going through the mental process of converting itself into an amphibious force, events on the coast of the Gulf of Mexico were providing them with the tools they would need to make it into a reality. Attempts to build prototype amphibious tractors by Vickers and tank designer J. Walter Christie had proven to be failures. Nevertheless, Marine officers were on the lookout for landing boats and other equipment that would be required for their new kind of warfare. Then, in 1937, they found an answer in, of all things, LIFE magazine.

The genesis of this new vehicle was a series of hurricanes that hit South Florida in 1926, 1928, and 1932. The storm damage made rescue and recovery of victims difficult in the flooded areas, low marshes, and swamps of the Okeechobee region. Seeing what he thought was a humanitarian need, financier and industrialist John A. Roebling suggested to his son Donald, a wealthy and eccentric engineer in Clearwater, Florida, that he design a rescue craft that “would bridge the gap between where a boat grounded and a car flooded out.”

alligator 3

Another early Alligator version. Roebling carried out a number of design and detail changes on the vehicle that would eventually become so important to the Marine Corps. DOD photo

A member of one of America’s most famous and creative families (his grandfather, Col. Washington Roebling, had designed the Brooklyn Bridge), Donald Roebling went to work on his father’s vision in 1933 and finished what he called the “Alligator” in early 1935. It was innovative in a number of areas, including the use of lightweight aluminum for most of the vehicle’s structure. Built with a small cab at the front and a large, open bed at the rear, the Alligator was powered by a 92-horsepower Chrysler industrial motor that drove a cleated track system. The track system, patented by Roebling in 1938, could propel the vehicle both in the water and on land. Roebling spent the next two years testing the Alligator, rebuilding it a total of four times by 1937 into “Alligator 2.”

While it was agile and relatively fast from the beginning of testing, Roebling nevertheless took his time working the bugs out of the vehicle. Four feet shorter than the original Alligator, the new model was offered for commercial use to the oil industry and other users later that year.

It was this vehicle that caught the eye of the editorial staff of LIFE magazine the same year. Always on the lookout for the new and unusual, LIFE published an article on the Alligator in the Oct. 4, 1937, issue. The LIFE article proved to be the key to taking Roebling’s humanitarian vision and turning it into a keystone military technology used to defeat Japan in World War II.

 

Connections

Interestingly, the first U.S. officer to show interest in Roebling’s Alligator was Rear Adm. Edward C. Kalbfus, commander of the Pacific Fleet’s battleships. Showing the LIFE article to Maj. Gen. Louis McCarty Little, commanding general of the Fleet Marine Force, Kalbfus suggested that the Alligator might help with the Marines’ amphibious transport needs. McCarty then sent the article to USMC Commandant Maj. Gen. Thomas Holcomb, who immediately saw merit in evaluating the Alligator. Holcomb asked Brig. Gen. Frederick L. Bradman, president of the USMC Equipment Board at Quantico, Virginia, to investigate.

At the end of this impressive brass chain was Maj. John Kaluf, secretary of the Equipment Board, who drew the assignment to actually look over the Alligator. Heading down to Clearwater in March 1938, he evaluated the Alligator and shot 400 feet of movie film. His report so impressed his superiors that, in June, Holcomb ordered that a “pilot model” be purchased for “further tests under service conditions.”

 

Prototypes and Tests

The initial roadblock to acquiring a test vehicle was financial; the Navy’s Bureau of Ships did not see merit in the Alligator, and refused to fund the building of a prototype for the Marines. Roebling, however, convinced by the Equipment Board officers that his Alligator had real value, agreed to build what became his “Alligator 3” with $18,000 of his own money. By January 1940, Roebling had the design of the Alligator 3 finished, and completed the prototype in May of the same year.

lvt guadalcanal

LVTs approach the beach at Guadalcanal. U.S. Marine Corps photo

Eventually, the Bureau of Ships found money to allocate for the project, and the USMC ordered its first test amtrac. Ironically, when the test amtrac rolled out of Roebling’s Dunedin, Florida, workshop, his biggest problem was trying to return $4,000 to the U.S. government, because he came in under budget.

Delivered in the fall of 1940, the vehicle retained the aluminum hull of the earlier Alligators, was powered by a 120-horsepower Lincoln-Zephyr engine, and incorporated improvements suggested by the Equipment Board. It was immediately shipped to Quantico, Va., for testing, where it was assigned to take part in a series of amphibious exercises by the 1st Marine Brigade at Culebra in Puerto Rico.

 

Testing With the “Brute”

When the test amtrac arrived in Puerto Rico, it fortuitously fell into the able hands of a young officer named Capt. Victor H. “Brute” Krulak. Krulak was assigned to conduct the tests by the brigade commander, Brig. Gen. H.M. “Howlin’ Mad” Smith. Krulak, a legendary Marine who eventually rose to lieutenant general (his son Charles became the 31st commandant) had already made a significant contribution to the development of amphibious watercraft.

lvt-1 at tarawa

An LVT-1 heads for the beach at Tarawa. Though casualties were heavy, they could have been disastrous without the Amtracs. National Archives photo

While a China Marine in 1937, Krulak had photographed Japanese Daihatsu landing craft, with their unique bow ramps for unloading personnel, equipment, supplies, and vehicles. Forwarding his photos, drawings, and a report to Marine headquarters, Krulak found when he returned to the States in 1939 that his report had been filed away with a marginal note reading “the work of some nut out in China.” Undaunted, Krulak built a model of the craft, and took it and his report to Smith, who sent Krulak to New Orleans boatmaker Andrew Higgins. Krulak was thus the first link in the chain of personnel and events that created Higgins’ famous landing craft, the Landing Craft, Vehicle, Personnel (LCVP).

Krulak attacked the Alligator 3’s test program with the same zeal, running the vehicle through the shallows, reefs, and coastal waters, documenting defects and problems with the craft, and suggesting modifications and improvements. However, the basic soundness of the Roebling design excited almost everyone who got near the craft. One of the rare exceptions was Atlantic Fleet commander Adm. Ernest J. King, a man of titanic reputation and ill temperament. Invited to take a ride in the amtrac by Smith, the craft unfortunately grounded on a reef while being driven by Krulak. Viciously mad, King and his staff walked in their whites over the reef and through the shoals to the beach, aiming a profane flow of words at Krulak, Smith, the amtrac, and the USMC in general.

tarawa-lvt-on-the-beach

Beach secured, Marines shelter in the lee of an LVT (1) from sniper fire as they take a break. U.S. Marine Corps photo

Despite King’s unpleasant ride, the USMC decided to put the amtrac into immediate production, as the Landing Vehicle Tracked (Mark 1), or LVT (1). When Krulak handed over his report and test data to Col. W.W. Rogers in December 1940, the information helped create the formal design requirement for the LVT (1). By July 1941, the first of 100 LVT (1)s began to roll off the production line of Food Machinery Corporation (FMC – today part of BAE Systems) in Dunedin, Florida.

These first LVTs had a number of changes from the test amtrac, including a steel hull, a 146-horsepower Hercules V-6 motor, and mounts for a pair of machine guns. They could move through water at 4 knots, and crawl across land at 15 mph. Each could carry a 4,500-pound load of troops and cargo across most of the reefs and beaches that would be found in the Pacific.

In February 1942, with the Pacific War in full swing, the 1st Amphibian Tractor Battalion was formed in Dunedin, with the early production LVT (1)s equipping them. The 2nd Amphibian Tractor Battalion was formed the following month, with additional LVTs ordered after the first batch. Roebling’s Alligator was going to war.

 

Into Service: Guadalcanal and Tarawa

Originally, the USMC saw the LVTs primarily as cargo haulers for ship-to-shore transport of critical materiel like ammunition and medical supplies. In fact, this is how they were used at Guadalcanal late in 1942, where both of the battalions saw action. Later, the LVT units continued to support amphibious operations in the middle and upper Solomons. But their real glory would come as a result of one more encounter with Krulak.

In May 1943, Krulak was called to headquarters in Noumea for another LVTrelated task. Higher headquarters wanted a truly extensive test of the LVT’s capability for operating over coral reefs in heavy surf to find out if they could support planned invasions in the Central Pacific. Krulak requisitioned a pair of LVT (1)s, loaded each with 5,000 pounds of dead weight, and spent a day of tortuous testing in the local reef waters. Both amtracs performed well in waves up to 6 feet. Satisfied at their capability, Krulak submitted his report and thought nothing more of it until November 1943.

tarawa lvt-1 and lvt-2

LVT-1s and an LVT-2 (foreground) on a beach, possibly Tarawa. U.S. Marine Corps photo

Planners for the invasion of the Gilbert Islands had been concerned over the poor quality of hydrographic data on hand, especially that for reef and tidal conditions around Betio Island. Part of the Tarawa atoll, the island of Betio was scheduled to be the first of the Japanese islands in the Central Pacific to be invaded. Fortified and manned by almost 5,000 Japanese, Betio was a target full of unknowns, and the decision was made to include 125 amtracs in the transport force.

When the 2nd Marine Division assaulted Betio on Nov. 20, 1943, the first 1,500 Marines were transported in the LVTs, which then made numerous trips between the transports offshore and the beach, bringing supplies and fresh Marines, and evacuating the wounded. Sadly, the worst fears of the U.S. planners had come true with the appearance of a neap tide at H-Hour, which made landing by any craft but the LVTs nearly impossible. During the Betio assault, the LVTs provided the only reliable transport between the Navy task force offshore and the Marines ashore.

Casualties were heavy, and 92 of the LVTs were knocked out. Worse, 180 Marines in the amtrac units were killed. The amtrac’s lack of armor plating had been a shortcoming, but only the LVTs had been able to keep operating over the reefs at Betio.

However, every major amphibious landing for the rest of the war would be led by a phalanx of LVTs, in numbers and varieties that Pete Ellis, Donald Roebling, and even Brute Krulak could not have imagined. All told, more than 18,000 LVTs were manufactured, in both LVT (personnel) and LVT(A), or armored, variants, the first of which was the LVT(A)1, with an M3 Stuart light tank turret mounting a 37mm gun.

AAV7s exercise

Marines from Charlie Co. 2nd Assault Amphibious Battalion, 31st Marine Expeditionary Unit, demonstrating amphibious capabilities unique to the United States Marine Corps during exercise Cobra Gold 11, Jan. 23, 2011. With the cancellation of the Expeditionary Fighting Vehicle, the Marine Corps is seeking solutions to retain those unique amphibious capabilities. U.S. Marine Corps Photo by PFC Nathaniel Henry

More than 8,300 of the LVTs manufactured were the LVT 4 version, which had improved armor protection, a rear ramp to allow personnel to exit under cover instead of having to jump over the side exposed to enemy fire, and additional firepower. Its armored cousins, almost 1,900 LVT (A)4s, were armed with turreted 75 mm howitzers and machine guns to provide gunfire support to landing forces on the surf line. Flamethrowers were also fitted to a few, but most LVTs remained troop carriers, and in that role they excelled throughout the Pacific War.

But these were hardly the last models in the amtrac line. Today the AAV7 is the backbone of the Marine amtrac fleet, and while the AAV7 fleet is being modernized, the Marine Corps is also looking for a replacement to continue providing Marines and other forces a way over the reefs, to the beach, and beyond.

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John D. Gresham lives in Fairfax, Va. He is an author, researcher, game designer, photographer,...