The navy is pushing to pay in yearly instalments for the two submarines it is buying, despite heavy criticism.

The national budget expenditure bill, before the House of Representatives, includes the navy's contentious plan to purchase two subs from China worth 22.5 billion baht.

The purchase is part of the 200-billion-baht defence budget being considered by a House scrutiny panel.

The first payment was supposed to have been approved last year but was postponed so the money could be used to fight the Covid-19 pandemic.

The navy is back at the House to defend the spending again. Navy spokesman Chettha Jaipiam insisted the force was duty-bound to do so.

"It's a matter of procedure," Adm Chettha said, noting that whether the spending will be passed or not is a separate issue. "There is no ulterior motive," he said.

The navy was aware of opposition to the defence budget and its plan to acquire the subs.

"We face resistance whenever the issue is brought before the committee," Adm Chettha said.

If the lawmakers insisted the procurement was premature, there was nothing the navy could do.