They were based on the Royal Navy's Bridgewater-class sloops, but with a heavier armament and omitting the minelaying equipment of the British ships.

470 tons of oil were carried giving a range of 6,000 nautical miles (11,000 km; 6,900 mi) at 11 knots (20 km/h; 13 mph).

[2][3] Armament consisted of three 120-millimetre (4.7 in) guns in single mounts on the ship's centreline, with two forward and one aft.

Four 2-pounder (40 mm) pom-pom anti-aircraft (AA) guns were fitted, while four depth charge throwers provided an anti-submarine armament.

As part of this programme, a contract was placed with the British shipbuilder Hawthorn Leslie for two sloops, to be named Gonçalo Velho and Gonçalves Zarco.