After yesterday’s Catalina catastrophe, I began to wonder what the biggest floatplane ever built was. Not a flying boat, where the aircraft’s fuselage also serves as a monohull with pontoons providing sea-keeping stability, but literally a plane attached to floats. Then I came across the obscure Italian-built CANT Z.511, which seems to wears this crown.


Right off the bat you can tell it’s an incredible looking machine. Massive, too. With a 130 foot wingspan, gross weight of 75,000 pounds, cruising speed of 205 miles per hour and a range of 2,800 miles, the Z.511 was truly a hulking international hauler.

To make it all happen, she packed four Piaggio P.XII RC.35 radials that put out 1,500 horsepower each and sat atop a pair of massive floats that gave her incredible stability on the water, being able to operate in seven foot seas. Although being the biggest float plane ever built is impressive, her mission and origin is even more intriguing.

Designed by famed Italian aerospace engineer Filippo Zappata, who also designed one of the most beautiful airliners of all time, the Breda-Zappata BZ.308, the CANT Z.511 began life in the late 1930s as a game-changing aircraft that could carry mail, cargo and people from Italy to Latin America. These plans, along with so many others, drastically changed when World War II begun, with fascist Italy allying itself with Nazi Germany. As such, the Z.511 went from a practical machine that could possibly open up new commerce around the globe, to a weapon.


The Z.511 would become a multi-role long-range military aircraft, with maritime patrol and attack being its core missions. No less than a dozen .50 caliber machine guns were to be added to the sea-going beast, along with a 20mm cannon in its nose. A bomb-bay was configured where luggage would have gone. Between it and wing stations, up to 9,000 pounds of bombs could be carried on a single mission. For surface attack, four racks capable of carrying heavy air-launched torpedoes could be fitted. Alternatively, it seems that four manned torpedoes/midget submarines, known as “Maiale,” for special operations mission could also be carried, with their frogmen crews flying inside the aircraft’s cabin until it was time to deploy.

That’s right, the Z.511 was supposed to be a special operations mothership.

The huge prototype seaplane first flew in October of 1940 and it performed outstandingly well during test flights which continued for almost three years. One of which saw the aircraft takeoff at gross weight in five foot seas and 40 mile per hour winds without any trouble.


A fleet of Z.511s was envisioned with a slew of special missions in mind. Jailbreaking Italian soldiers being held on the Arabian Peninsula, a raid on British oil interests in the Persian Gulf, a propaganda mission to drop leaflets over New York City, a whistle-stop tour of Latin America and bombing missions on Soviet ports located along the Black Sea were all theorized for the unique aircraft. Yet the most interesting and high-priority of all missions, and one that was supposedly on track to occur in the summer of 1943, was an ultra long-range special operations raid on the Port of New York.


Oh, it gets weirder.

Although the accuracy of data on the Z.511’s short career remains questionable, and facts remain hard to confirm, a long-range raid utilizing the aircraft was supposedly deep in the planning stages by spring of 1943. The Z.511 would carry four manned torpedoes/midget submarines, with two frogmen per submarine, all of which would surrender, go down fighting or kill themselves once the raid had concluded as there was no way to return back to the Z.511 for a flight back to Italy.

The Z.511 would leave from Nazi occupied France and refuel along its route over the Atlantic via U-boats, of which their support for the operation had been supposedly obtained by May of 1943. By that time, Italian commandos had volunteered and been trained for their one-way mission as well. With all these pieces in place, the raid was said to have been planned for late June of 1943.


This all changed (assuming any of it actually was planned in the first place) when an attack on the Z.511’s base at Lake Trasimeno occurred just weeks before the mission was supposed to occur, with Allied fighters raking the huge aircraft with their machine guns. As a result, the raid was supposedly pushed back, but then in July Mussolini was arrested and the Italian Armistice was signed, marking an end to any plans for such a raid. So much for that idea.

Shortly after, the only flying Z.511 was destroyed by its own keepers to keep it from falling into both German and Allied hands. The other prototype, which was still in pieces at the time of the first aircraft’s demise, was supposedly scrapped by Axis forces so that its metal could be recycled and used to feed the then struggling Nazi war machine.


And that is the short, strange and murky life story of the world’s largest floatplane (at least that I know of), and the tale of what would have been one of the Axis Powers’ most daring long-ranged strategic attacks on American interests along the East Coast of the entire war.

Even if the story of the raid has been embellished over time, the sheer size and capability of the Z.511 remains no less amazing.

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