The Navy announced it has relieved the captain who sounded the alarm about an outbreak of COVID-19 aboard the USS Theodore Roosevelt.

Capt. Brett Crozier, who commands the Roosevelt, an aircraft carrier with a crew of nearly 5,000, was relieved of his command Thursday, but he will keep his rank and remain in the Navy.

Full coverage of the coronavirus outbreak

Crozier raised the alarm this week, sending a strongly worded letter to Navy leadership that detailed his concerns about the spread of the virus on the ship. The letter leaked to the media and generated a series of headlines.

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Speaking at a news conference Thursday evening, Acting Navy Secretary Thomas Modly said Crozier was removed from his post because he sent the letter over "non-secure unclassified email" to a "broad array of people" rather than up the chain of command.

"I have no doubt in my mind that Captain Crozier did what he thought was in the best interest of the safety and well-being of his crew," Modly said. "Unfortunately, it did the opposite. It unnecessarily raised the alarm of the families of our sailors and Marines with no plans to address those concerns."

Capt. Brett Crozier of the USS Theodore Roosevelt. U.S. Navy

Modly insisted the that decision was his alone. He praised Crozier but said he had concluded that the captain "allowed the complexity of the challenge of the COVID breakout on the ship to overwhelm his ability to act professionally."

"The responsibility for this decision rests with me," Modly added. "I expect no congratulations for it. Captain Crozier is an incredible man."

In a statement, a group of top Democrats on the House Armed Services Committee sharply criticized the decision to remove Crozier.

“The dismissal of Captain Crozier at this critical moment, as the sailors aboard the U.S.S. Theodore Roosevelt are confronted with the COVID-19 pandemic, is a reckless, political move that reeks of undue command influence," read the statement from chairman Rep. Adam Smith of Washington, subcommittee chairs Rep. Joe Courtney of Connecticut, Rep. John Garamendi of California and Rep. Jackie Speier of California.

Former Vice President Joe Biden also blasted the Navy's acting secretary in a statement, saying that he "shot the messenger — a commanding officer who was faithful to both his national security mission and his duty to care for his sailors, and who rightly focused attention on a broader concern about how to maintain military readiness during this pandemic."

The ship, which was operating in the Pacific, pulled into port in Guam last week several days after multiple crew members tested positive for the virus. By Wednesday, there were 93 positive test results, and more than 1,000 people were taken off the carrier and placed into isolation on Guam. In total, 2,700 people are expected to disembark the ship this week, with a smaller crew remaining to maintain the carrier.