President Trump Nominates Mark Esper As Next US Defense Secretary

Mark Esper previously served as Army Secretary (Picture: US Department of Defense). 

President Donald Trump has asked the US Senate to confirm Mark Esper as the successor to former defence secretary Jim Mattis.

Mr Esper had been carrying out the role in an acting capacity since Patrick Shanahan resigned last month. 

The US has not had a permanent defence secretary since General Jim Mattis stepped down in December - the longest period in the Pentagon's history.

It is believed Mr Mattis resigned over President Donald Trump's decision to pull US troops out of Syria.

In a statement, the Pentagon said that, by law, Mr Esper's nomination on Monday means he is no longer acting defense secretary.

The military veteran has returned to his previous position of Army Secretary, the statement said.

Navy Secretary Richard Spencer has been chosen to fill in as the acting defense secretary.

Mr Spencer's tenure as acting secretary is expected to be brief, as Mr Esper could be confirmed in the role as early as Thursday.

Mr Esper spent 10 years on active duty in the US Army and fought in the First Gulf War. 

He also served in the National Guard and Army Reserve for 11 years.

After retiring from the military in 2007, Mr Esper went into politics, working as a senior policy advisor to former Senator Chuck Hagel.

He later became policy director for the House Armed Services Committee and national security advisor for Senate Majority Leader Bill Frist.

During George W Bush's administration, he served as the Deputy Assistant Secretary of Defense for Negotiations Policy at the Pentagon.

He has also worked as a commissioner on the US-China Economic and Security Review Commission.

Prior to the Trump administration, only twice before has the defence department been led by an acting secretary, most recently in 1989 - it has never had more than one in a single year.

The lack of stability in the Pentagon has raised questions in Congress at a time of heightened tensions with Iran and continued US wars in Afghanistan and Syria.