WASHINGTON, Jan 16 (Reuters) - U.S. Defense Secretary Lloyd Austin's aide asked for the ambulance picking up the Pentagon chief to keep its lights and sirens off during a New Year's Day call to 911, according to audio of call obtained by Reuters.

"Can the ambulance not show up with lights and sirens? We're trying to remain a little subtle," the aide, whose name was redacted from the audio, told the 911 dispatcher.

Austin's trip to Walter Reed National Military Medical Center and subsequent hospitalization was kept secret for days, including from U.S. President Joe Biden and even Austin's deputy, Kathleen Hicks.

He spent two weeks in the hospital due to complications from a Dec. 22 prostate cancer surgery - which was also kept secret - and was discharged on Monday to his Virginia home.

Austin's secrecy triggered a political uproar. Republicans seized on the incident to accuse Austin, a retired four-star general who led forces in Iraq who is America's first Black defense secretary, with dereliction of duty.

Some prominent Republicans, including Donald Trump, called for Austin to be removed from his job.

Biden said on Friday he had confidence in Austin despite what the president agreed was a lapse in judgment.

It remained unclear why Austin, 70, decided against informing senior Biden administration officials about his cancer and post-surgical complications, even when they required his hospitalization.

The audio from the 4-1/2-minute call was released to Reuters by the Fairfax, Virginia county office that processes Freedom of Information Act requests.

The aide who called 911 told the dispatcher that Austin did not feel like he might pass out and was not disoriented or confused. The aide asked whether the ambulance in Virginia might be able to take him to Walter Reed, which is located in Bethesda, Maryland.

The Defense Department's Inspector General's office has said it will begin a review this month of the handling of Austin's hospitalization.

Photo from Reuters