The Rolls-Royce engine used in the Lockheed L-1011 TriStar was the RB211.
The RB211 is a family of high-bypass turbofan engines developed by Rolls-Royce for wide-body civil aircraft. Lockheed selected the RB211 for the L-1011 TriStar, which used three engines: two mounted under the wings and a third installed in the rear fuselage with an S-shaped intake duct.
The engine program became a major episode in Rolls-Royce history. Development difficulties and cost pressures contributed to the company's entry into receivership in 1971, after which Rolls-Royce was nationalized. The RB211 eventually became an important commercial engine family and helped establish the company's long-term position in large civil turbofans.
The RB211 should not be confused with the Trent family, which developed later from related technology and powers many newer airliners. Nor was the TriStar a twin-engine aircraft: its three-engine layout was central to its design and certification era.