From interwar sloops to modern offshore patrol vessels

What were interwar sloops, and do modern offshore patrol vessels perform a similar role?

Sloops were flexible small warships for escort, ASW, gunboat, and policing work, and many modern OPVs fill comparable missions.

The term did not merely preserve an age-of-sail category. Interwar sloops were the smallest vessels the Royal Navy still treated as warships, and treaties left designers unusual freedom over their form. They could be heavily armed for combat or lightly equipped for patrol and policing, with anti-submarine and gunboat duties between those poles. River-class offshore patrol vessels and similar OPVs now occupy much of the old sloop's functional space.