COSAG used gearboxes and clutches so steam turbines, gas turbines, or both could drive the shafts. Steam offered cruising efficiency and reliability, while gas machinery supplied rapid starting and acceleration. The arrangement also appeared in County-class destroyers and the Spanish aircraft carrier Dédalo, making it a broader experiment beyond the Type 81s. Steam and gas turbines depend on different engineering, fail under different conditions, and follow different maintenance cycles. COSAG joined useful operating qualities at the price of a demanding propulsion and support system.
Chapter · 26:16-29:05
Why COSAG burdened Type 81 engineering
COSAG let Type 81 frigates use steam, gas, or both, but combining two turbine technologies imposed difficult gearing, maintenance, and failure-management demands.