The BAE 57 mm system is a qualitative improvement over 40 mm, but the financial and integration step is much larger than the move from 30 to 40 mm. The Royal Navy must keep the River class visibly and functionally distinct from the Type 31 or politicians may treat the cheaper hull as an equivalent substitute. Even after receiving the larger gun, the patrol ship would still lack the frigate's full sensors, systems, endurance in combat, and force role. The design choice begins with mission and fleet structure rather than the maximum weapon that can fit on deck.
Notable Point · 3:02:15-3:05:12
A 57 mm gun changes the patrol-ship cost equation
A 57 mm gun offers a real capability increase over 40 mm, but its larger cost jump makes an OPV look more like a cheap frigate without delivering Type 31 capability.