Seaplanes were a lifesaver in the Pacific theater in World War II, in more ways than one. U.S. PBY-4 Catalinas picked up downed fliers floating in the ocean, flew search missions to detect enemy ships, and hunted submarines. In the vastness of the Pacific Ocean, where airfields were scattered and at a time when aerial refueling hadn’t been invented, the ability to land and take off on the water made seaplanes indispensable.
However, seaplanes also tended to be heavy, awkward, and inferior in performance to land- and carrier-based aircraft. Though the Soviets flew some models such as the Be-12 amphibious patrol plane during the Cold War, seaplanes mostly faded from military use.
But seaplanes are now coming back. A second Pacific War – this time against China – would be fought over long stretches of ocean devoid of airfields. Even worse, airbases might be destroyed or damaged by long-range weapons such as Chinese ballistic missiles. Japan already operates the well-regarded US-2 seaplane which has proven useful for missions such as rescuing aircrews floating in the water.
Now, the U.S. military also wants a seaplane. In fact, it wants a seaplane so big that it can haul armored vehicles. The potential benefits for a giant cargo seaplane are enormous. Troops and equipment could be ferried to places that lack airfields, or where the airbases have been knocked out by enemy bombardment. Or, amphibious armored vehicles could be airlifted into remote locations for surprise attacks.
The Liberty Lifter and the Caspian Sea Monster
The very name of the project – the “Liberty Lifter” – seems as evocative of World War II as Rosie the Riveter. But DARPA, the Pentagon’s research agency, actually envisions a modern aircraft.
The issue is that U.S. forces rely on sealift for bulk transportation and logistics.
“Although very efficient in transporting large amounts of payload, traditional sealift is vulnerable to threats, requires functional ports, and results in long transit times,” notes the DARPA solicitation.
“Traditional airlift is orders of magnitude faster, but is expensive with limited ability to support maritime operations. Additionally, aircraft require long prepared runways or suffer payload limitations typical of Vertical Takeoff and Landing (VTOL) or other maritime aircraft,” the solicitation adds.
The solution is an aircraft that can operate from the water. But more than that, DARPA seeks a design that utilizes ground effect, in which an aircraft takes advantage of the lift generated by an aircraft’s wings when the plane flies close to the ground. The most famous example is the Ekranoplan – also known as the “Caspian Sea Monster” – a giant 300-ton, 242-foot-long ground-effect aircraft armed with anti-ship missiles that was more boat than an airplane.
However, merely copying the Ekranoplan won’t do.
“These vehicles were high speed (250+ knots) and runway independent, but controllability of in-ground-effect flight limited operations to calm waters (e.g., the Caspian Sea),” DARPA explained. “Additionally, high-speed operation in ground effect increases the likelihood of collision in congested environments with limited options for safe maneuvers.”
DARPA seems to be aiming for a sort of hybrid design that combines traditional seaplanes with ground effect aircraft. Whatever design finally emerges, it’s going to be big. DARPA’s specifications include the capacity to carry two U.S. Marine Corps Amphibious Combat Vehicles, or six Twenty-Foot Equivalent Container Units. That suggests an aircraft with the dimensions of an Air Force C-17 transport.
Other specifications of the Liberty Lifter are equally impressive: A cargo capacity of 90 tons, which is about the capacity of a C-17; an operational range of more than 4,000 nautical miles while carrying a 45-ton cargo; and a ferry range greater than 6,500 nautical miles; finally, the ability to operate at altitudes over 10,000 feet.
The aircraft must be capable of taking off and landing in waters up to sea state 4 (moderate seas), achieve ground effect flight up to sea state 5 (moderately rough waters), and move on the water up to sea state 5. It must also perform “sustained unpressurized flight out of ground effect to enable avoidance of bad weather and obstacles, flight over some landmasses, and operational flexibility”
Interestingly, the Liberty Lifter must be capable of “on-water float for up to 4-6 weeks at a time,” according to DARPA. This suggests an aircraft/boat that can operate in remote areas without fixed airfields, and serve as a floating base for special operations troops or intelligence missions.
Seaplanes and guns
Significantly, DARPA doesn’t mention armament for the Liberty Lifter. Perhaps that’s because seaplanes in World War II had a mixed combat record. Aircraft like the Catalina were useful for anti-submarine patrol or attacks on undefended merchant ships. But the additional weight of their flotation gear hampered their combat performance: Imperial Japan’s floatplane version of the famed A6M2 Zero was a poor dogfighter.
However, the U.S. Air Force is planning to arm cargo planes, such as the C-130, with cruise missiles. Transports have a huge capacity to carry munitions, and stand-off weapons allow the lumbering craft to remain safely out of range of enemy air defenses. A missile-armed Liberty Lifter would be a powerful weapon. But even as an unarmed transport, a seaplane that can haul armored vehicles to remote locations would be an enormous asset.
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