Type 31 gun choices and the presence mission

Is the Type 31's 57 mm gun a sensible choice?

Yes for a lower-cost presence ship facing low-level threats; task-group air-defence and picket ships need a different, more specialized weapons fit.

A 57 mm gun and two 40 mm weapons are a sensible fit for a globally deployed presence frigate handling piracy, small boats, and constricted waterways. The Type 31 needs enough firepower to manage those lower-level threats without carrying the cost of a high-end specialist escort. In wartime, not every frigate should serve as a distant picket. Some escorts protect carriers or amphibious ships at close range, where a dense short-range gun battery has a different value. The proposed fit follows the ship's presence and task-group roles rather than forcing every vessel into the same armament pattern.