Gen Theerachai Nakwanich will likely become the new army chief while Gen Preecha Chan-o-cha, the prime minister's brother, will be defence permanent secretary, according to a source.
In coup-plagued Thailand, the army chief position is considered the most coveted and influential one in the country, since it involves commanding a 200,000-strong armed force. Other positions, while on the same payscale, are not as much sought after, including the permanent secretary post.
It has been a tight race. Both generals will retire next year, meaning the October 2015 reshuffle is their only chance of commanding the army.
Army chief Udomdej Sitabutr reportedly nominated Gen Theerachai, his classmate, as his successor after two meetings with Defence Minister Prawit Wongsuwon, the source said.
Gen Prawit, who is also a deputy prime minister, fully supports Gen Theerachai as they both served at the 2nd Infantry Division Queen's Guard. Gen Theerachai was also commander of Army Region 1 when the May 22, 2014 coup was staged. After the putsch, he also headed the peacekeeping force, commanding all troops, the source said.
"The PM doesn't want his brother to become a political target. His records would be scrutinised and old wounds will be used against him, which may eventually affect Gen Prayut himself.
"Being a prime minister's brother will surely invite all sorts of attacks while Gen Prayut will have to be PM for at least two more years," the source said.
The source was referring to a controversial land sale and the public funds found in his wife's bank account which made headlines earlier.
Gen Theerachai was nominated for army chief. (Bangkok Post file photo)
Gen Prawit, however, said: "The PM has no say on this. He just told the committee which I chair to select the best person."
Earlier, there were rumours of a counter-coup if Gen Preecha was not appointed because for the country's leader, an unrelated leader of the army cannot be trusted as much as one's own blood.
But Gen Prayut said early this week he had no fear for such a threat. In fact, he would gladly welcome anyone to take his seat.
There might be another reason for the general's indifference. The source said in practice Gen Prayut already has a tight rein on the army. After all, all commanders at present are the men close to either him, Gen Prawit or Interior Minister Gen Anupong Paochinda.
"And these three musketeers will never fall out," the source said.
For the navy, chief Adm Kraisorn Chansuvanich nominated assistant naval chief Adm Narongpol Na Bangchang to take his seat.
Since Adm Narongpol is also chairman of the submarine committee, he is expected to steer through the project and prepare the navy for the new hardware as soon as the government approves it.
There will be no change at the top at the air force this year since commander-in-chief ACM Treetod Sonjance will retire next year.
For the Royal Thai Armed Forces Headquarters, formerly known as the Supreme Command, commander Gen Vorapong Sanganate nominated chief of staff Gen Sommai Kaodeera as his successor.
A defence ministry source said on Wednesday the reshuffle list of all armed forces had already been submitted to Gen Prawit, as chairman of the defence reshuffling committee, before the Aug 15 deadline.
The committee by law consists of seven ex officio members: the defence minister, his deputy, the supreme commander, the commanders of the three armed forces and the defence permanent secretary.
In practice, it now comprises six persons because Gen Udomdej holds both the positions of deputy defence minister and army chief.
The committee will vet the lists and vote on the final ones to be submitted to the prime minister for endorsement.