Happy Friday and welcome to Overnight Defense. I'm Ellen Mitchell, and here's your nightly guide to the latest developments at the Pentagon, on Capitol Hill and beyond. CLICK HERE to subscribe to the newsletter.

THE TOPLINE: Defense Secretary Mark Esper Mark EsperTop admiral: 'No condition' where US should conduct nuclear test 'at this time' Overnight Defense: Trump hosts Israel, UAE, Bahrain for historic signing l Air Force reveals it secretly built and flew new fighter jet l Coronavirus creates delay in Pentagon research for alternative to 'forever chemicals' Oldest living US World War II veteran turns 111 MORE said he is open to reinstating the Navy captain who was removed from his post last week shortly after asking for help with a coronavirus outbreak aboard his ship.

"We've taken nothing off the table," Esper said on CBS News Friday morning. "My inclination is always to support the chain of command, and to take the recommendations seriously."

The background: Capt. Brett Crozier, as commander of the USS Theodore Roosevelt, sent a letter to Esper pleading for help with an outbreak on the ship. That letter was eventually leaked to the media, which led to Crozier's removal.

Acting Navy Secretary Thomas Modly resigned Tuesday after the release of transcripts and audio of an inflammatory speech a day earlier in which he said Crozier was either "naive" or "stupid" for taking the actions he did.

The Pentagon is actively investigating Crozier over the letter.

"There are always extreme cases where going outside the chain of command makes sense. That's why we want to see where this investigation takes us," Esper said.

The biggest challenge: Several Navy hospital ships have been sent around the country to alleviate the burden on medical facilities, including in New York City. Esper said Friday that what "keeps him up at night" is maintaining enough medical staff to battle the virus.

"The biggest challenge is the medical staff, is making sure you have sufficient doctors and nurses," he said. "For me, because I have these mobile capability inherent in the military, is to maintain adaptability and be agile."

TRUMP NAMES ARMS CONTROL ENVOY AS TREATY'S EXPIRATION LOOMS: President Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE has officially named Marshall Billingslea as his special envoy for arms control, a role expected to spearhead efforts to reach a nuclear agreement with Russia and China.

The White House announced Billingslea's appointment in a news release Friday, roughly a month after reports surfaced that Billingslea was chosen.

The appointment comes as the United States' current agreement with Russia, known as the New START Treaty, expires in less than a year.

Expiration date nears: The agreement, which was negotiated by the Obama administration, caps the number of deployed nuclear warheads the United States and Russia can have at 1,550 a piece. There are also limits on deploying weapons, such as intercontinental ballistic missiles, that could deliver the warheads. And the treaty lays out a verification regime that includes 18 on-site inspections per year.

The agreement expires Feb. 5, 2021, but there is an option to extend it another five years after that.

The hold up: Arms control advocates have urged Trump to immediately extend the agreement, arguing that letting it lapse would mean no legal constraint on the world's two largest nuclear arsenals for the first time in five decades.

But the Trump administration has said it wants to expand the scope of the agreement, including adding China and new Russian weapons systems. Russia has offered to extend the treaty immediately with no pre-conditions, while China has repeatedly rejected joining talks.

Who is Billingslea?: Billingslea is currently the assistant Treasury secretary for terrorist financing.

He was previously nominated to be under secretary of State for civilian security, democracy and human rights in 2018, but his confirmation stalled as Democrats and advocates raised questions about his role in the George W. Bush administration interrogation program now widely viewed as torture.

Billingslea oversaw conditions of detainees at Guantanamo Bay in 2002 and 2003. A 2008 Senate report said he advocated interrogation techniques Congress later outlawed as torture.

In his confirmation hearing for the human rights role, Billingslea said he would "advocate for and respect" Congress's 2015 decision to ban torture.

Pushback: Senate Foreign Relations Committee ranking member Sen. Bob Menendez Robert (Bob) MenendezKasie Hunt to host lead-in show for MSNBC's 'Morning Joe' Senators ask for removal of tariffs on EU food, wine, spirits: report VOA visa decision could hobble Venezuela coverage MORE (D-N.J.) blasted Billingslea's appointment as arms control envoy.

"Mr. Billinsglea has a troubled history with the Senate Foreign Relations Committee," Menendez said in a statement Friday. "Following his unsuccessful nomination for the State Department's top human rights post, serious questions remain concerning whether he was forthright and truthful when testifying before the committee about his role in the detainee torture scandal during the Bush administration."

Menendez also highlighted that jobs traditionally tasked with leading arms control negotiations that require Senate confirmation -- including under secretary of State for arms control and international security and assistant secretary of State for arms Control, verification and compliance -- have been vacant for months.

"This terrible decision is emblematic both of this administration's willingness to sidestep the Senate's constitutionally-mandated role of nominee advice and consent, and the haphazard, careless way the administration treats nuclear diplomacy," Menendez said.