The Rolls-Royce Gem is a turboshaft engine developed specifically for the Westland Lynx helicopter in the 1970's. The design started off at Bristol-Siddeley as the BS.360.

Its 3-shaft engine configuration is rather unusual for turboshaft/turboprop engines. Basic arrangement is a 4-stage axial compressor, driven by single stage IP turbine, supercharging a centrifugal HP compressor, driven by a single stage HP turbine. Power is delivered to the load via a third shaft, connected to a 2-stage free (power) turbine. A reverse flow combustor is featured.

Gem 42 develops 1,000 shp at Take-off, Sea Level Static, ISA, but the Maximum Contingency Rating is 1,120 shp.

Until recently all versions of the Lynx have been Gem powered. However, now that Rolls-Royce own Allison, they have been marketing the more modern LHTEC T800, developed jointly with Honeywell. The civil version, known as the CTS800, will power the AgustaWestland Super Lynx.

Helicopters | Aircraft engines