High Quality Content by WIKIPEDIA articles! The de Havilland PS.23 or PS.52 Gyron, originally the Halford H-4, was Frank Halford`s last turbojet design while working for de Havilland. Intended to outpower any design then under construction, the Gyron was the most powerful engine of its era, producing 20,000 lbf (89 kN) "dry", and 27,000 lbf (120 kN) with afterburner ("reheat" in British terminology). The engine was actually too large for most roles and saw no production use. It was later scaled down to 45% of its original size to produce the de Havilland Gyron Junior, which was somewhat more successful.