The Saunders-Roe SR.45 Princess was a British flying boat aircraft developed and built by Saunders-Roe at their Cowes facility on the Isle of Wight. It has the distinction of being the largest all-metal flying boat to have ever been constructed.
The Princess had been developed to serve as a larger and more luxurious successor to the pre-war commercial flying boats, such as the Short Empire. It was intended to serve the transatlantic route, carrying up to 100 passengers between Southampton, United Kingdom and New York City, United States in spacious and comfortable conditions. To achieve this, it was decided early on to make use of newly developed turboproptechnology, opting for the in-developed Bristol Proteus engine to power the aircraft. The project suffered delays due to difficulties encountered in the development of the Proteus engine. On 22 August 1952, the first prototype Princess, G-ALUN, conducted its maiden flight. Between 1952 and 1954, the first prototype performed a total of 47 test flights, including two public appearances at the Farnborough Airshow.
Work on the Princess was ultimately cancelled after having produced three examples, only one of which flew. By the mid-1950s, large commercial flying boats were being increasingly overshadowed by land-based jet airliners. Factors such as runway and airport improvements had added to the viability of land-based aircraft, which did not have to compromise to accommodate the additional weight and drag of the boat hulls that were necessary on seaplanes, or the mitigating measures needed against the corrosion caused by seawater. Following the project's termination, the three airframes were stored with the intention of selling them on; however, upon receipt of a promising offer for the aircraft, it was found that corrosion had set in while in storage. As a result, all three airframes were scrapped.