Why a warship might retain fixed-pitch propellers

Why would a warship avoid controllable-pitch propellers?

The additional controls must justify their maintenance and damage risks, especially where an anti-submarine ship's acoustic performance depends on a carefully optimized propeller.

Controllable pitch adds linkages and controls that must survive shock and battle damage. Extra maintenance, spares, and repair time can reduce the practical benefit of greater maneuvering control. The panel also considers how changing shaft revolutions or adding moving mechanisms could affect a frigate's acoustic signature. An anti-submarine ship may have a fixed propeller carefully optimized for quiet running. The comparison with an azimuth pod concerns repair access: a complete pod can be exchanged in dry dock, while pitch-control linkages extend into the hull. The balance depends on the ship's mission and the reliability of the complete installation.