Her Majesty’s Nuclear Seaplane

Steve Weintz
War Is Boring
Published in
6 min readOct 22, 2013


Doomed luxury airliner almost had an atomic second life


She was a dazzling aircraft, a great winged hope of postwar Britain, the largest all-metal flying boat ever built. Her design incorporated brand-new technologies: a pressurized cabin, all-hydraulic controls and turboprop power. Yet even as she took to the skies over the 1953 Farnborough Air Show, the Saunders-Roe S.R.45 “Princess” was an anachronism built to serve a vanishing Empire.

Saunders-Roe, a firm with a long and distinguished history in seaplane design, responded to the Ministry of Supply’s 1945 request for a passenger flying boat to serve the postwar Transatlantic route.

The proposed seaplane’s range of more than 5,000 miles would also bring India and the Far East much closer to London. Following the May 1946 order for three planes, Saunders-Roe began construction at its Cowes plant on the Isle of Wight.

The huge aircraft — nearly as large as the legendary Spruce Goose — was to carry more than 100 passengers in cruise-liner style: two decks, private cabins, lounges, dining rooms and staff quarters.

The three fuselages built were so big they had to be jacked down and tilted to get them out of the hangar, in order to fit the 10 turboprop engines into the wings. The Bristol Proteus engines were to supposed to produce a combined 30,000 horsepower, enough for the Princess to cruise at nearly 400 miles per hour at 40,000 feet.

Above — interior design for the Princess flying boat. Illustration via Fly Historic Wings. At top — The Saunders Roe S.R.45 Princess in flight. RuthAS photo via Wikimedia

The few men to fly the Princess remarked on what an easy, agile plane it was to fly. On Aug. 22, 1952, company test pilot Geoffrey Tyson was so pleased with the Princess’ taxi-testing performance on the Solent that he took the plane into the air on an impromptu swing around the sky, to the delight of company officials.

At the Farnborough Air Show that September, another Princess flyover amazed attendees, who would have been even more amazed had they known the plane lost hydraulic power and was kept flying level and straight by some keen piloting.

But though Princess Elizabeth ascended to the throne as Queen, the Princess did not become queen of the skies. Before the first aircraft was completed its intended customer, BOAC, decided that flying boats had no place in the company’s future. The RAF expressed interest in the three huge planes for transport use, but backed away as estimates of maintenance costs mounted.

The prospect of maintaining 10 engines along with fighting saltwater corrosion on the world’s biggest seaplane hull proved too rich for British aviation. Indeed, the British Empire began to die the year the Princess tender was offered in 1946, when an exhausted Britain turned to the U.S. to fight Communists in Greece, and the torch of rule passed west.

Now without a purpose, the one flying and two nearly-completed planes were placed in storage to await interest; and in 1956 interest came from a seaport on the other side of the world, from another country’s military.

Like the U.S. Air Force, the U.S. Navy was keenly interested in nuclear-powered flight, and was already operating a small mobile reactor aboard the USS Nautilus. Convair, maker of the legendary PBY Catalina flying boat, was hard at work on its big R3Y Tradewind turboprop seaplane and the F2Y Sea Dart seaplane fighter, and exploring all sorts of exotic seaplane concepts.

The Air Force’s atom-plane test efforts involved a highly-modified B-36 bomber with a reactor in its stern bomb bay and a 12-ton lead-and-rubber capsule for the crew. Convair modified its own product into the NB-36 “Convair Crusader” and gained valuable experience in the process.

The NB-36 didn’t actually fly on nuclear power; rather it tested various shielding concepts for flight-crew protection. During a series of test flights over West Texas and New Mexico, the NB-36 was accompanied by a battalion of airborne Marines in case it crashed and the site had to be secured.

So when the U.S. Navy approached Convair with a really weird idea, the San Diego aircraft maker responded with alacrity. If the Princess flying boats were brought to America, asked the Navy, could Convair convert them to nuclear power? Yes, said the company, and drew up blueprints for the modifications. Like the Convair Crusader, the nuclear Princess would be a testbed for atomic-powered flight and crew shielding.

Convair blueprint for the nuclear-powered Princess. Photo via Scott Lowther

All that room prepared for Imperial dignitaries and posh travellers would accommodate a Pratt & Whitney liquid-metal-cooled reactor, a heat exchanger and some serious plumbing to run superheated (radioactive) air into special P&W gas turbines; the “hot” gas would replace gas heated by jet fuel once the big plane reached cruising altitude.

Four jet engines would get the seaplane airborne while two nuclear turbojets would take over during cruise. The great weight of the nuclear power system played to the flying boat’s strength — it’s easier to float great weights than land them on runways. The Air Force’s planned nuclear bomber would have required a 3-mile long runway, as long as the Space Shuttle’s.

Alas, a second half-life for the Princess was not to be. Atomic aircraft soon went the way of flying boats and the three giant planes remained wrapped in plastic wrap awaiting a future.

The Space Age almost rescued them; Aero Spacelines, the firm that created the wild “Super Guppy” cargo planes to transport Saturn rocket stages, tried to buy the seaplanes in 1966, but when they were unwrapped it was found that corrosion had rotted the frames. All three planes were scrapped before Apollo 11, and like the Martin P6M SeaMaster, all that remains today are wing floats and a couple of parts.

The Princess and her even grander proposed siblings are now a part of the Imperial past.



Steve Weintz
War Is Boring

Writer, filmmaker, artist, animator. Former firefighter, archaeologist, stuntman.