This new mounting had a shield with a sharply raked front, to allow increased elevation (to 55 degrees), contrasting noticeably with the vertical front of the previous CP Mark XVIII, and easily differentiated the S class onwards from their immediate predecessors.

Savage was the exception in this respect, being fitted with four 4.5 in guns; a twin mounting forward and two singles aft.

These ships used the Fuze Keeping Clock HA Fire Control Computer.

Known as the "Hazemeyer" (or "Haslemere"), this advanced mounting was tri-axially stabilised in order that a target could be kept in the sights on the pitching deck of a destroyer and was fitted with an analog fire control computer and Radar Type 282, a metric range-finding set.

The Hazemeyer design had been brought to Britain by the Dutch minelayer Willem van der Zaan that had escaped from the German occupation in May 1940.