President Donald Trump fired Veterans Affairs (VA) Secretary David Shulkin and nominated White House doctor Ronny Jackson to replace him in the wake of a bruising ethics scandal and a mounting rebellion within the agency.
A Navy rear admiral, Dr Jackson is a surprise choice to succeed Mr Shulkin, a former Obama administration official and the first nonveteran to head the VA.
Mr Trump had been considering replacements for Mr Shulkin for weeks but had not been known to be considering Dr Jackson for the role.
In a statement, Mr Trump praised Dr Jackson as "highly trained and qualified".
It was a decision that signalled Mr Trump chose to go with someone he knows and trusts, rather than the candidate with the longest resume, to run a massive agency facing huge bureaucratic challenges.
Dr Jackson has served since 2013 as the physician to the president, and gained a national profile earlier this year for holding a sweeping press conference on the president's health.
Mr Trump has selected Robert Wilkie, the under secretary of defence for personnel and readiness, to serve as the acting head of the VA.
It is the government's second largest department, responsible for nine million military veterans in more than 1,700 government-run health facilities.
The selection of Mr Wilkie bypasses VA deputy secretary Tom Bowman, who has come under criticism for being too moderate to push Mr Trump's agenda of fixing veterans' care.
Mr Shulkin had continued to insist he had the full confidence of the White House amid continuing investigations over his travel and leadership of the department.
He had agreed to reimburse the government more than 4,000 dollars after the VA's internal watchdog concluded last month that he had improperly accepted Wimbledon tennis tickets and that his then-chief of staff had doctored emails to justify his wife travelling to Europe with him at taxpayer expense.
Mr Shulkin also blamed internal drama at the agency on a half-dozen or so political appointees who were rebelling against him and Bowman, insisting he had White House backing to fire them.
It was the latest in a series of departures for top administration officials, including secretary of state Rex Tillerson, who was fired by Mr Trump earlier this month.
The sudden departure comes as Mr Trump is seeking to expand the Veterans Choice programme, a campaign promise that major veterans' groups worry could be an unwanted step towards privatising VA health care.
His plan remains in limbo after Congress declined last week to include it in a spending bill.
Having pushed through legislation in Mr Trump's first year making it easier to fire bad VA employees and speed disability appeals, Mr Shulkin leaves behind a department in disarray.
Several projects remain unfinished, including a multibillion-dollar overhaul of electronic medical records aimed at speeding up waiting times for veterans seeking medical care as well as expanded mental health treatment for veterans at higher risk of suicide.