Marsun M21 class are a class of 10 Patrol Boat currently commissioned by the Royal Thai Navy. The M21 class has an overall length of 21.4 m, an overall beam of 5.56 m, and a hull draught of 1.05 m. It is powered by two MAN diesel engines driving two fixed pitch propellers, and can attain top speeds of more than 30 kt and a range of more than 350 n miles (648 km) at economical speed. The vessel has carrying capacity for up to 4,000 litres of fuel, 1,200 litres of water, and can accommodate a crew of nine. It can operate up to Sea State 2. Marsun has delivered over 260 various types of vessels, these include Fast Patrol Craft, Fast Attack Missile Craft, Crew and Supply Vessels.
Marsun M21 have been equipped with a 20 mm cannon in the primary position. The class is also armed with one 12.7 mm machine gun with a co-axial 81 mm grenade launcher in the aft section. The M21 class has also been equipped with one crane-launched rigid hull inflatable boat (RHIB) at stern, and one inflatable life raft canister on the port side at aft. Once delivered, all 11 vessels are expected to be deployed with the RTN’s coastguard squadron and take on duties such as VIP escorts, fishery resources protection, and other maritime constabulary duties in the Andaman Sea and the Gulf of Thailand.