Although similar in layout, boats of the second series featured a slightly larger displacement and more powerful machinery.

Propulsion consisted of two diesel engines powering two shafts for a total of power output of 3,000 hp (2,200 kW), enabling a speed of 17 knots (31 km/h; 20 mph) and range of 1,000 nmi (1,900 km; 1,200 mi) at 12 knots (22 km/h; 14 mph).

During the 1970s the first series underwent modernization which included the removal of the 3"/50 caliber gun in favor two five-barrelled Soviet-made RBU-1200 rocket launchers with the addition of a Tamir-11 sonar.

[2] The last boat of the series, PBR-512, was decommissioned in 1972 and sunk as a target ship in 1983 in the vicinity of the Bay of Kotor.

The boat was finally cut loose and sunk in the Žanjic cove to a depth of 25 m (82 ft).

[3][4] The Kraljevica boats proved to be the most widely exported ship class built by SFR Yugoslavia.

A total of eleven boats were transferred to countries of the Non-Aligned Movement of which Yugoslavia was one of the founding members.