Deputy defense secretary Kathleen Hicks was NOT told Lloyd Austin was in intensive care unit in hospital (despite taking on his duties as Pentagon chief)

Defense Secretary Lloyd Austin's mystery hospitalization was a secret kept even from his deputy Kathleen Hicks, it has been revealed.

Austin, 70, is in the spotlight after failing to tell the White House about planned surgery which left him in the ICU on New Year's Day due to complications.

Now it's emerged he also did not tell his second-in-command Hicks until Thursday, even as she assumed some of his responsibilities two days before. 

Austin ranks just below Biden at the top of the chain of command in the US military, and his duties require him being available at a moment's notice.

Hicks was on vacation in Puerto Rico when Austin went in for surgery, but she was not informed about it until days later, after she had been asked to work while on holiday. 

Defense Secretary Lloyd Austin's mystery hospitalization was a secret kept even from his deputy Kathleen Hicks, it has emerged. (Pictured: Austin and Hicks at a Pentagon briefing)

Austin, 70, ranks just below President Joe Biden at the top of the chain of command of the US military and his duties require him being available at a moment's notice to respond to any manner of national security crisis

US Defense Secretary Lloyd Austin (pictured) is likely to keep his job despite apparently failing to inform the president that he was having surgery and going AWOL for five days, according to former officials

Pentagon Press Secretary Maj. Gen. Pat Ryder told CNN it was 'not uncommon' for the secretary to transfer some responsibilities - but added that she wasn't aware of the reason she was stepping in on this occasion. 

A spokesperson for the department told DailyMail.com that Austin 'resumed his full duties' from Walter Reed National Military Medical Center on Friday evening. 

He was still in the hospital but 'recovering well' by Sunday morning, the spokesperson added. 

They declined to disclose any details about the surgery citing 'medical and personal privacy issues'. 

Despite a barrage of criticism against Austin from members of Congress about his mysterious disappearance, White House aides have told Politico that his job is not in jeopardy. 

Several also highlighted Biden's deep personal connection with Austin, due to the former four-star general's close friendship with the president's late son Beau Biden. 

The officials, who spoke with Politico on condition of anonymity, said that a senior Pentagon aide will likely loose their job over the chaos.  

'Someone's head has to roll,' one former defense employee said. 

'Someone made the decision not to disclose,' another ex-official agreed. That person will likely be gone shortly.'

'Not telling the [White House], Congress or the media he is sick, and then telling Pentagon staff he is working from home is next level. This is a problem.' 

Some officials also noted that Alabama-born Austin was close with Beau Biden, after they served in Iraq together and attended Catholic services alongside each other.  

Lower-level aides including Sasha Baker and his deputy Kathleen Hicks have been sitting in for Austin in the interim. Hicks was reportedly on vacation in Puerto Rico but had to step in for some duties. 

Despite a barrage of criticism from members of Congress and the media about Austin's mysterious disappearance, White House aides have told Politico that his job is not in jeopardy

A spokesperson for the department told DailyMail.com that Austin 'resumed his full duties' from Walter Reed National Military Medical Center (pictured) on Friday evening

Five days after the top national security official dropped off the radar, Pentagon Press Secretary Maj. Gen. Pat Ryder (pictured) gave a limited explanation about his absence

Five days after the top national security official dropped off the radar, Pentagon Press Secretary Maj. Gen. Pat Ryder gave a limited explanation about his absence.

'On the evening of January 1, Secretary of Defense Lloyd J. Austin III was admitted to Walter Reed National Military Medical Center for complications following a recent elective medical procedure,' Ryder said. 

'He is recovering well and is expecting to resume his full duties today. At all times, the Deputy Secretary of Defense was prepared to act for and exercise the powers of the Secretary, if required.'

Just a day earlier, Ryder held a televised news briefing that conveyed the sense of business as usual at the Pentagon, offering Austin's condolences to ally Japan following its New Year's Day earthquake, for example. 

But the past week has been anything but normal for the Pentagon, with U.S. troops in the Middle East wrestling with the regional fallout from the unfolding Israel-Hamas war and carrying out a U.S. retaliatory strike in Baghdad on Thursday.

The way the Defense Department handled Austin's hospitalization stands in contrast to how the State Department dealt with then-Secretary of State Colin Powell's prostate surgery on Dec. 15, 2003.

The State Department spokesman at that time issued a statement in the morning making public that Powell, a retired four-star general and former chairman of the Joint Chiefs of Staff, was in surgery at Walter Reed Army Medical Center and would remain there for several days before returning home.

Ex-DOD officials have said someone is likely to be fired over the kerfuffle - though Austin might be saved thanks to his personal connection with Joe Biden. (Pictured: Biden speaking during a White House meeting in January 2023, flanked by Austin and Antony Blinken)

Some officials who spoke with Politico on condition of anonymity said that a senior Pentagon aide will likely loose their job over the chaos. (Pictured: the Pentagon seen on August 27, 2023) 

It also said Powell would be on a reduced schedule while he recovered from the operation. The State Department's spokesman at the time, Richard Boucher, then offered details on Powell's surgery in his daily briefing.

Boucher, contacted by Reuters on Friday, said the key question regarding public disclosure was whether Austin was under anesthesia or was incapacitated.

'Was there any moment in the process where he could not function as secretary of defense?' he asked. 'If you are up and walking around and have your information and you have your aides in the next room and you can make split-second decisions... then there is probably not a public necessity to disclose.

'The only necessity is if you are going to be conked out,' he added.