Why the sloop-frigate boundary blurred

Had the line between sloops and frigates blurred by the 1950s?

Yes, and the blurring was already underway in the 1940s; construction standards and anti-submarine roles were part of the distinction.

The sloop-frigate boundary was deliberately blurred before the 1950s and was already indistinct during the 1940s. Sloops could perform frigate-like work while being built to naval standards. Frigates were often produced to more hybrid civilian-naval standards for mass anti-submarine work. The labels therefore reflected construction practice and institutional history as well as operational role.