All troops will soon be required to be vaccinated against COVID-19, the Pentagon announced Monday afternoon.

Defense Secretary Lloyd Austin will request a waiver for the mandate from President Joe Biden by mid-September unless the U.S. Food and Drug Agency fully approves the Pfizer vaccine ahead of then, which Austin said is likely.

“Get the shot. Stay healthy. Stay ready,” Austin said in a memo sent to troops Monday. “All FDA-authorized COVID-19 vaccines are safe and highly effective. They will protect you and your family. They will protect your unit, your ship and your co-workers, and they will ensure we remain the most lethal and ready force in the world.”

Last week President Joe Biden asked Austin to consider how the coronavirus vaccine could be added to the multitude of other required shots service members receive.

“Secretary Austin and I share an unshakable commitment to making sure our troops have every tool they need to do their jobs as safely as possible,” Biden said in a prepared statement. “These vaccines will save lives. Period. Over 350 million shots have been given in the United States alone. We cannot let up in the fight against COVID-19, especially with the delta variant spreading rapidly through unvaccinated populations.”

Military installations including Fort Carson, Peterson Space Force Base, Schriever Space Force Base, the Air Force Academy and Buckley Space Force Base in Aurora — roughly 45,000 strong — have been tasked with presenting their implementation plans on how they would vaccinate their service members.

“I have every confidence that service leadership and your commanders will implement this new vaccination program with professionalism, skill and compassion,” Austin said in the memo.

At the same time, the Department of Defense is developing policies regarding additional restrictions and requirements for unvaccinated troops and civilian employees.

“We are working hard on what will be a policy directive to come in the coming days to make it clear what those requirements and restrictions are and how they apply to everybody in the … workforce including uniformed personnel,” John Kirby, Pentagon press secretary, said during a Monday news conference.

The Defense Department is also keeping an eye on infection rates and the highly transmissible delta variant of the coronavirus.

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“I will not hesitate to act sooner or recommend a different course to the president if l feel the need to do so,” Austin said. “To defend this nation, we need a healthy and ready force. I strongly encourage all military and civilian personnel — as well as contractor personnel — to get vaccinated now and for military service members to not wait for the mandate.”

Mandatory inoculations are nothing new for the military. The first on record were ordered by Gen. George Washington in 1777, mandating inoculation of his Continental Army against small pox after an outbreak thinned its ranks. Since then, troops have been routinely vaccinated against diseases from anthrax to yellow fever.

The coronavirus vaccine was initially handled differently because the Food and Drug Administration had authorized its use on an emergency basis. Because of the emergency status, the Pentagon allowed troops to decide whether they would get vaccinated.

Given the choice, many troops, especially younger enlisted service members, shunned the vaccine, Pentagon statistics show.

The Pentagon has said more than 1 million service members are fully vaccinated and another 237,000 have had one shot of a two-shot series.

Stephen Brady, a spokesman for Peterson and Schriever Space Force bases, said they will be ready.

“Peterson and Schriever Space Force bases are capable of meeting the vaccination requirement through vaccination lines, the same process we use to administer the annual flu vaccine,” spokesman Stephen Brady said. “Many of the service members stationed here have already voluntarily received the COVID-19 vaccination. We will spend the coming weeks to ensure we are prepared to meet the mandate.”

The Air Force Academy also plans to make sure its personnel are vaccinated.

“As soon as the vaccine is mandated, the Academy will ensure that the required service members are administered the vaccine in a timely fashion,” spokesman Dean Miller said.

Emails seeking comment from Fort Carson and Buckley Space Force Base weren’t immediately returned. 

The Pentagon feels the roughly five-week turnaround is plenty of time for military installations to act.

“We don’t believe the inventory is going to be a problem,” Kirby said. “That’s one of the reasons the secretary is giving the services a couple of weeks to come back with their implementation plans.”

The shift from a voluntary to mandatory vaccine is likely to cause pushback from some in the service and it is unknown how refusal to obey this order may be punished, leaders said.

“You can consider this memo today as what we would call in the military a warning order,” Kirby said. “A warning order to the force that this is coming and we want you to be ready for it as well. And obviously we prefer that you get the vaccine now and not wait for the mandate.”

U.S. Rep Adam Smith (D-Wash.), Chairman of the House Armed Services Committee, voiced support for Austin’s plan to mandate vaccines.

“As the pandemic continues to ravage our communities, and with the rising threat of the delta variant, it is imperative that our service members are protected from this deadly, invisible threat,” Smith said. “The science is clear: Vaccination is the only way to beat this virus. As such, Secretary Austin’s decision to make COVID-19 vaccination mandatory for our entire force is going to save lives and safeguard our military readiness.”

The Department of Defense will announce implementation plans once they are fully developed.