The SR.45 "Princess" was a large flying boat, being the largest all-metal flying boat to have ever been constructed. The Princess featured a rounded, bulbous, "double-bubble" pressurized fuselage which contained two full passenger decks; these decks had sufficient room to accommodate up to 105 passengers in great comfort. The planing bottom of the hull had only a slight step in the keel to minimize drag in the air. The Princess was powered by an arrangement of ten Bristol Proteus turboprop engines. These engines drove six sets of four-bladed propellers; of these, the inner four propellers were double, contra-rotating propellers which were driven by a twin version of the Proteus, named the "Bristol Coupled Proteus", each engine drove one of the propellers. The two outer propellers were single and each powered by a single engine.