Why heavily arming River-class OPVs could cost the Royal Navy frigates

Could the next generation of Royal Navy offshore patrol vessels be upgraded with a 4.5-inch gun?

The objection is budgetary: a frigate-like fit risks having patrol ships counted against the frigate force, while lighter guns are considered a possible upgrade.

Royal Navy offshore patrol vessels support fisheries protection, diplomatic contact, presence patrols and maritime-security partnerships. Forward deployment builds local relationships that can help larger naval forces operate in the same region. The vessels stationed in Southeast Asia and the Pacific are connected here with the ability to send carrier groups to the Far East and demonstrate global reach. Fitting a 4.5-inch or five-inch gun, or missiles, risks encouraging budget officials to count patrol vessels as substitutes for frigates. A proposed 57 mm gun and possible close-in weapon system would increase armament while keeping it sufficiently light to preserve that distinction.