A contract for the vessels was signed on 14 July 2015 at the RTN head office in Bangkok, Marsun's head of marketing, Theerabhat Sroisena, said in response to queries from IHS Jane's. The RTN currently operates three M21-class patrol boats, the which were delivered by Marsun in May 2013.
According to specifications provided by the shipyard, the M21 patrol boat is 21.4 m long, has a beam of 5:56 m, and a draft of 1:05 am , Powered by two MAN diesel engines driving two fixed pitch propellers, the vessel has top speeds in excess of 30 kt, a range of 350 n miles, and an endurance of 24 hours. It can a accommodate nine crew and can carry 4,000 liters of fuel and 1,200 liters of water.
The aluminum-hulled platform is equipped with X-band radar, and has one bow-mounted Denel GI-2 20 mm gun as its play weapon. The vessel Also carries a stern-facing 12.7 mm machine gun with a co-axial 81 mm grenade launcher. It also can Embark one rigid hull inflatable boat.
Like the previous three vessels, the boats are Likely to be deployed primarily for exclusive economic zone (EEZ) patrolling and other Constabulary and protection duties with the RTN's Coast Guard Squadron.
An M21-class patrol boats currently in service with the RTN. The country ordered four more of the vessels in July 2015.