Prime Minister Prayut Chan-ocha has approved a 200-million baht project to design a mini-submarine - the first step in the planned construction of a prototype for the Royal Thai Navy.

The design will take an estimated four years, with construction of the prototype expected to take another two years at an expected cost of another one billion baht.

Capt Sattaya Chantharaprapa, deputy commander of the Royal Thai Navy Academy and head of the mini-submarine research project, announced the prime minister's decision on Tuesday.

Under the plan, the design will take four years and construction of the first mini-submarine another two years, to be followed by seaworthiness checks and training for one year, or a total of seven years, Capt Sattaya said.

The actual cost of the mini-submarine, also known as a midget-sub, would be known after four years, but it was expected to be about one billion baht. 

Capt Sattaya said the navy began the mini-submarine project in October last year. Twenty-five navy officers, all graduates in European countries in naval architecture and other fields, were sent for training in England.

Gen Prayut had floated the idea to build the mini-submarine. About 193 million baht had been allocated for the research work, Capt  Sattaya said.  

The first mini-submarine in the still unofficially named “Chalawan Class’’ would have a surface displacement of 150-300 tonnes, a crew of 10 and a 300 nautical miles range, he said.

The announcement is the latest move in the government's plan for a submarine fleet to match those of Thailand's maritime neighbours.

In April last year, the Prayut cabinet endorsed the navy's purchase of a Yuan Class S26T submarine from China at a cost of 13.5 billion baht, part of the planned procurement of three of the submarines at a total cost of 36 billion baht.