WASHINGTON (AFP) - President Barack Obama has chosen a submarine officer to serve as the next head of the US Navy and an infantry officer who commanded troops in Afghanistan for army chief, officials said Wednesday.

Admiral John Richardson, currently the head of naval reactors, has been nominated to lead the navy, and General Mark Milley, who also served in Iraq, was picked to lead the army.

In announcing the nominations, Defence Secretary Ashton Carter praised Milley as "a warrior and a statesman" who had the intellect and battlefield experience to take the helm of the US Army.

"Mark and I flew to Herat a day after an attack on the US consulate there. And I saw Mark take command of the scene and stand with our people there," said Carter, recounting a visit to Afghanistan.

"I was impressed by his candor and good judgement. And I knew right away that he had even more to offer to the United States Army."

Milley, a graduate of Princeton University, worked as head of the International Security Assistance Force's Joint Command in Afghanistan and was asked to review the delicate case of Sergeant Bowe Bergdahl, who was held captive by insurgents in Afghanistan for five years.

After a methodical study of the case, Milley decided Bergdahl should be charged with desertion.

If confirmed by senators, Milley will succeed General Raymond Odierno, who is due to retire in the coming months.

Obama's pick for the navy is the second consecutive submarine officer to be named to the post, underscoring the importance attached to subs despite their exorbitant cost.

If confirmed by the US Senate, Richardson will face a budget battle over the funding of the next class of ballistic missile submarines, which cost an estimated US$4.9 billion (S$6.5 billion) a piece.

To avoid disrupting other ship-building plans, officials have already suggested new submarines will need to be paid for partly outside of the annual Pentagon budget and will need a special long-term funding plan.

Carter called Richardson "a bold thinker, a tremendous leader and the go-to officer for many of the Navy's tough issues in recent years."

As head of the navy's nuclear propulsion program, Richardson faced questions last year about an alleged cheating scandal among sailors training on reactors.

The current head of the navy, Admiral Jonathan Greenert, is due to retire later this year.