The Counties and Tribal-class frigates gave the Royal Navy operational evidence about whether first-generation marine gas turbines were dependable enough for future warships. Under COSAG, gas turbines supplied rapid high power while steam turbines provided efficient long-range cruising. Either plant could still move the ship if the other technology proved unreliable, making the mixed installation an insurance policy as well as a propulsion choice. The price was a complicated chain of clutches, reduction gears, and combining gearboxes between turbines and propeller shafts, with many opportunities for mechanical loss. Experience nevertheless showed advantages substantial enough for HMS Bristol's Type 82 design to retain COSAG. The episode illustrates how the service accepted temporary complexity to learn safely before committing later classes to gas turbines.
Notable Point · 20:20-23:11
County-class COSAG tested gas turbines without sacrificing range
Combined steam-and-gas propulsion let the Royal Navy test high-power gas turbines while retaining efficient steam cruising, range, and mechanical insurance.