Prime Minister Prayut Chan-o-cha, who is also defence minister, defended the army's 7-billion-baht tank procurement from Ukraine.
He was responding to questions raised by Pheu Thai MP Saranwut Saranket during the censure debate on Thursday.
Mr Saranwut asked why the tank purchase had not been done as a government-to-government deal and if Ukraine had been fined for the four-year delay in delivery.
Another issue raised by Mr Saranwut was whether the tanks purchased were brand new or used.
Gen Prayut said the question of whether this deal should be a government-to-government contract was to be discussed between the two countries, but then it was dropped because the purchase was made through a company that acted as a country representative.
As for the delay in delivery, he put it down to conflicts in Ukraine at the time.
Meanwhile, Deputy Defence Minister Chaichan Changmongkol said the tanks, which had been replaced by the new ones purchased from Ukraine, were outdated and kept breaking down after six decades in service.
He also pointed out that the tank-procurement project had kicked off in 2011, before the coup-maker National Council for Peace and Order came into being in 2014.
The delay was caused by the Russian military presence in Ukraine, which was why Thailand chose not to demand any compensation, he said, insisting the tanks were brand new.
Gen Prayut, meanwhile, denied the opposition's accusation that he had taken a team of 35 officials to just inspect tanks, saying the trip had served other purposes too.
He said he had been invited by the Ukrainian government, and decided to inspect the tanks while he was there.
Gen Prayut also countered allegations that the army was buying more weaponry to ramp up its capabilities in preparation for a coup in the future, by saying the armed forces were actually downsizing.
He said the army has been introducing more technology in their operations in order to save on resources and manpower, while delivering better military performance.
The prime minister added that every purchase of weapons was done carefully within the available budget, adding that the military has not gone on a spending spree to purchase what it pleases.
He also said that the price of weapons may seem steep, but they had been bought with long-term maintenance schemes.