In 1945, Saunders-Roe was asked by the British Ministry of Supply to bid for a long range civil flying boat for British Overseas Airways Corporation (BOAC), who planned to use them on transatlantic passenger services. Saunders-Roe's bid was successful, and it received an order for three aircraft in May 1946.
The Princess was powered by ten Bristol Proteus turboprop engines, powering six propellers. The four inner propellers were double, contra-rotating propellers driven by a twin version of the Proteus, the Bristol Coupled Proteus; each engine drove one of the propellers. The two outer propellers were single and powered by single engines. The rounded, bulbous, 'double-bubble' pressurized fuselage contained two passenger decks, with room for 105 passengers in great comfort.
The ailerons and rudder were split into multiple sections such that if a part of the servo-powered control system failed the faulty section could be "trailed" so that it did not act against the working sections. The planing bottom of the hull had only a slight step in the keel to minimize drag in the air.
In 1951 BOAC changed its mind about its needs and decided it had no requirement for the Princess. It was announced that construction of the three aircraft would continue as transport aircraft for the RAF. However, in March 1952, it was announced that while the first prototype would be completed, the second and third would be suspended to await more powerful engines. The prototype, G-ALUN, first flew on 22 August 1952 and was flown by test pilot Geoffrey Tyson off the Solent. A planned two-three hour flight was curtailed because of erroneous readings on airscrew bearing temperature. Three more flights followed in that week and then it appeared at Farnborough that year.
G-ALUN was the only one to fly - making 46 test flights in total, about 100 hours flying time. It appeared at the Farnborough Airshow in 1953.
Two other Princesses (G-ALUO and G-ALUP) were built, but they never flew. After a number of years in mothballs, two at Calshot Spit, awaiting further use, NASA considered using them as heavy-duty freight aircraft for transporting Saturn V rocket components. Aquila Airways offered £1 million pounds each for the Princesses in 1954. The nascent Airbus consortium thought of using two for transporting A300 fuselage sections, but opted to use Super Guppies instead. All three Princesses were broken up in 1967.
They were the last fixed-wing commercial aircraft produced by Saunders-Roe. The company built one more fixed-wing design, the Saunders-Roe SR.53 mixed-power (rocket and turbojet) fighter design; aside from that, the company concentrated on helicopters and hovercraft after this point.
Whilst the prototype aircraft had advanced (but conventional) hydraulic controls, S-R intended production aircraft to use an analogue system based around electrical servos with hydraulic final control actuators. Such a system was built and ground-tested, but the Princess project was cancelled before any aircraft was fitted with the system.