Defense Secretary Lloyd Austin on Wednesday ordered all U.S. service members be vaccinated immediately for COVID-19.

The country’s top military official announced the order in a memo in which he ordered service leaders to “impose ambitious timelines for implementation,” according to the Associate Press.

Over 800,000 service members have yet to get their shots, according to Pentagon data reviewed by the wire service.

Like other organizations and businesses, the Pentagon acted after the Food and Drug Administration earlier this week gave full approval to the Pfizer vaccine. The COVID-19 vaccine adds to the list of required shots troops must get as part of their military service.

Austin didn’t order a specific timeline for completing the vaccinations but said the military services will have to report regularly on their progress, the Associated Press also reports. 

“To defend this Nation, we need a healthy and ready force,” he said in the memo. “After careful consultation with medical experts and military leadership, and with the support of the President, I have determined that mandatory vaccination against coronavirus disease … is necessary.”