It is an upgraded version of the Rade Končar missile boat class and is 8.5 metres (28 ft) longer.

The Kralj class was developed by the Brodarski institut (BI) from Zagreb for the Yugoslav Navy as a successor to the Končar-class missile boats.

The first ship in the new class was to have a pennant number RTOP-501 and named Sergej Mašera after Sergej Mašera, an officer of the Royal Yugoslav Navy who died preventing the destroyer Zagreb from falling in Italian hands during the Axis invasion of Yugoslavia.

At the start of the Croatian War of Independence, the first ship in the class was nearing completion at the Kraljevica Shipyard.

A second, slightly modified ship was laid down by Croatia during the 1990s and commissioned in the early 2000s as Kralj Dmitar Zvonimir (RTOP-12).