WASHINGTON - President-elect Joe Biden introduced retired general Lloyd Austin as his pick for Secretary of Defence on Wednesday (Dec 9), responding to criticism that his choice would erode a norm meant to ensure civilian control of the military, and that Mr Austin might not pay sufficient attention to the Asia-Pacific region.

Mr Austin, who retired from the military more than four years ago, will require a waiver from Congress to be confirmed to the post. Under American law, a former military officer must have been out of uniform for at least seven years before becoming Secretary of Defence.

"There are good reasons for this law that I fully understand and respect, and I would not be asking for an exception here if I did not believe this moment in our history didn't call for it - and if I didn't have the faith I do in Lloyd Austin to ask for it," Mr Biden said at the media event in Wilmington, Delaware.

The incoming President had high praise for Mr Austin, who headed the US Central Command under President Barack Obama from 2013 to 2016 and oversaw the withdrawal of 150,000 American troops from Iraq.

If confirmed, Mr Austin would be the first African American to head the Defence Department, in line with Mr Biden's goal to bring greater diversity to his Cabinet.

Mr Biden and Mr Austin also stressed that the retired general valued the importance of America's allies, including those in the Asia-Pacific.

Their comments came after some consternation that a commentary penned by Mr Biden in The Atlantic in support of Mr Austin on Tuesday failed to mention the region entirely, raising questions about whether Mr Austin would have the interest in engaging allies and partners in the region or competing with China.

"I understand the important role the department plays in maintaining stability, deterring aggression, and defending and supporting critical alliances around the world, including in the Asia-Pacific, in Europe, and around the world," said Mr Austin, adding that he shared Mr Biden's belief that America was strongest when it worked with allies.

"Over the years, I've worked hand-in-hand with our diplomatic colleagues and our partners around the globe, and witnessed firsthand what we're able to accomplish, together. And, if confirmed, I look forward to resuming this important work," he added.

In his speech, Mr Biden also stressed that Mr Austin would uphold the principle of civilian leadership over the military, saying that he had faithfully carried out the orders of civilian leaders during his time as general.

"There is no doubt in my mind whether this nominee will honour, respect, and on a day-to-day breathe life into the pre-eminent principle of civilian leadership over military matters in our nation," said Mr Biden, urging Congress to grant the waiver.

On his part, Mr Austin stressed that he would come into the role as a civilian leader with a deep appreciation and reverence for the prevailing wisdom of civilian control of the military.

"I recognise that being a member of the president's cabinet requires a different perspective and unique responsibilities from a career in uniform. I intend to keep this at the forefront of my mind," he said on Wednesday.

This waiver was granted only in 1950, for General George Marshall, and in 2017 for retired General James Mattis, who had been out of uniform for four years at that point.

News of Mr Austin's nomination, which broke on Monday, was greeted with some dismay from national security experts and discomfort by several lawmakers.

While they acknowledged his impressive credentials, they also voiced concerns about military culture influencing senior civilian leadership, as well as his ties to the defence industry. Mr Austin sits on the board of aerospace and defence company Raytheon Technologies.

Dr Kori Schake, a national security expert at the American Enterprise Institute and a Republican former defence official who endorsed Mr Biden this year, said the circumstances did not support a waiver for Mr Austin. Granting him one would make it "an accepted practice instead of rare exception", she said on Twitter.

AEI visiting fellow Eric Sayers also criticised Mr Biden for effectively forcing Congress to weigh the historic nature of appointing the nation's first African American defence secretary against upholding the principle of civilian pre-eminence over the military.

It remains to be seen how Democrats in Congress will lean, particularly given the vocal opposition among some to granting Mr Mattis a waiver in 2017.

He was confirmed 81 to 17 in the Senate and 268 to 151 in the House. But several high-profile Democrats, including former presidential hopefuls Elizabeth Warren and Kirsten Gillibrand, were on the record as either voting no or vocal about their reluctance.

On Tuesday, Democrat Congresswoman Elissa Slotkin of Michigan wrote on Twitter that she felt apprehensive about having "another recently retired general to serve in a role designed for a civilian", even though she deeply respected Mr Austin.

Ms Slotkin, a former senior Defence Department official who worked together with Mr Austin while he was in the military, said: "The job of secretary of defence is purpose-built to ensure civilian oversight of the military. That is why it requires a waiver from the House and Senate to put a recently retired military officer in the job."

"And after the last four years, civil-military relations at the Pentagon definitely need to be rebalanced. Gen Austin has had an incredible career -- but I'll need to understand what he and the Biden Administration plan to do to address these concerns before I can vote for his waiver," she added, in a sentiment voiced by other Democrats.

Mr Austin's nomination was supported by others, however, notably former defence top official Michele Flournoy who had been previously seen as a frontrunner for the post.

In a statement congratulating Mr Austin on Tuesday, she said: "I know he will bring his impressive skills to bear to lead all those who volunteer to defend our country, military and civilian, at this critical moment in our nation's history."