1. The Type 23 is fitted with a Combined Diesel Electric And Gas Turbine (CODLAG) Propulsion System installed as a twin shaft arrangement. Each shaft set comprises one Rolls Royce SPEY SM1C Gas Turbine (GT), double reduction gearing, one DC Electric Motor (EM), wound on the gearbox output shaft, shafting and a high skew fixed pitch propeller (Type B). The shafts can only be driven astern using the electric motors (EM Drive).

For ahead movements, the shafts may be driven in two different modes: via EM Drive (as for astern), or in CODLAG Drive when both electric motors and gas turbines contribute to the ahead power provided. In CODLAG Drive the bias or contribution of the EM motors, and therefore the load on the Diesel Generators (DGs), may be adjusted from 0 - 100%. 0% EM bias effectively provides gas turbine drive in isolation.

2. The gearbox output shaft, EM motor and shafting are disconnected from the gearing when in EM drive, with the reduction gear elements and gas turbines stationary and Lub Oil system shut down for quiet operation. The gearbox has no reversing capability. Astern shaft movements are carried out using EM drive, with the GT drive disconnected via the synchronising self-shifting clutch (SSS clutch) within the gearbox.

3. Control of the propulsion machinery is from the Ship's Control Centre (SCC) in response to orders transmitted from the bridge via the propulsion order system. Facilities are provided for local control in machinery spaces for EMs, SSS Clutches, Shaft Brakes and GTs in the event of failure of the remote links.

4. The EM motors are powered, through thyristor power converters, by a combination of four 600V AV 12 Cylinder PAXMAN VALENTA Diesel Generators (DGs). The DGs also supply the ship's main Motor Generators (MGs) supplying the 440V power distribution system. Control of the 600V and 440V distribution systems is from the Primary Electrical Control Position (PECP) in the SCC, or Secondary Electrical Control Positions (SECPs) in the Fwd and Aft Switchboards.