"Riviere du Loup" was ordered 2 January 1942 as part of the 1942-43 modified Flower-class building programme. This programme was known as the Increased Endurance. Many changes were made, all from lessons that had been learned in previous versions of the Flower-class. The bridge was made a full deck higher and built to naval standards instead of the more civilian-like bridges of previous versions. The platform for the 4-inch main gun was raised to minimize the amount of spray over it and to provide a better field of fire. It was also connected to the wheelhouse by a wide platform that was now the base for the Hedgehog anti-submarine mortar that this version was armed with. Along with the new Hedgehog, this version got the new QF 4-inch Mk XIX main gun, which was semi-automatic, used fixed ammunition and had the ability to elevate higher giving it an anti-aircraft ability.