WASHINGTON (AP) — The Pentagon's initial allotment of coronavirus vaccine will be administered at 16 defense sites in the United States and abroad, with health care workers, emergency service personnel and residents of military retirement homes getting top priority, officials said Wednesday.

Next in line, once follow-on supplies of vaccine becomes available, will be military personnel who provide “critical national capabilities,” such as nuclear weapons crews and cybersecurity forces, as well as certain military units getting ready to deploy.

The vaccinations will be voluntary because the Pfizer vaccine initially is to be made available on an emergency use basis. The shots could become mandatory later if vaccines are fully licensed by the Food and Drug Administration, the officials said.

A few dozen of the Pentagon's leaders, including the acting defense secretary, Christopher Miller, and Gen. Mark Milley, chairman of the Joint Chiefs of Staff, are to be among those receiving early vaccinations, said Pentagon spokesman Jonathan Hoffman. Some of those leaders will get their shots in public in order to demonstrate the Pentagon's confidence in the vaccine's safety, he said.

Separately, officials said that as part of the military's continuing support for state and local governments fighting the pandemic, 45 military medical personnel will be sent to Wisconsin this week to support four civilian hospitals. They are acting on a request for assistance by the Federal Emergency Management Agency. Military medical personnel already are helping at hospitals in Texas and North Dakota.

The Pentagon is to received slightly fewer than 44,000 doses of the Pfizer vaccine initially, Hoffman said. The timing depends on when the FDA gives the go-ahead for distribution and use of the Pfizer vaccine.

In their first evaluation of the Pfizer vaccine, FDA scientists this week confirmed that it offers strong protection, setting the stage for the government to green light the biggest vaccination effort in the nation’s history. The FDA's independent advisers were to meet Thursday to debate whether evidence was strong enough to recommend vaccinating millions of Americans. A final FDA decision and the first shots could follow within days.

Thomas McCaffery, the assistant secretary of defense for health affairs, told a Pentagon news conference that although vaccinations will be voluntary, at least initially, he strongly recommends that all who are offered the shot take it. The first doses are to be ready for use within a day or two of the FDA go-ahead, he said.

“Our advice to everyone is to take the vaccine, just based on risk," said Lt. Gen. Ronald Place, director of the Defense Health Agency.

The initial set of 43,875 doses of the Pfizer vaccine are to be provided in varying quantities at 16 locations, with distribution to be vastly expanded later to reach all military members and Defense Department civilians when more doses become available.

The initial 16 sites are:

—Darnall Army Medical Center at Fort Hood, Texas.

—Wilford Hall at Joint Base San Antonio, Texas.

—Madigan Army Medical Center at Joint Base Lewis McChord, Washington.

—Womack Army Medical Center at Fort Bragg, North Carolina.

—Navy Branch Health Clinic at Naval Air Station Jacksonville, Florida.

—Base Alameda Health Services at the Coast Guard Base at Alameda, California.

—Naval Medical Center at San Diego (which also will distribute doses to the Naval Hospital at Camp Pendleton, California).

—Naval Hospital Pensacola, at Pensacola, Florida (which will distribute to the Armed Forces Retirement Home at Gulfport, Mississippi).

—Walter Reed National Military Medical Center at Bethesda, Maryland (which will distribute to the Armed Forces Retirement Home in Washington, D.C).

—Portsmouth Naval Medical Center at Portsmouth, Virginia (which will distribute to the Coast Guard Base Clinic at Portsmouth).

—Indiana National Guard at Franklin, Indiana.

—the New York National Guard Medical Command at Watervliet, New York.

Doses from the initial Pfizer batch of vaccine also will be administered at Tripler Army Medical Center in Honolulu and at three overseas locations: Allgood Army Community Hospital at Camp Humphreys in South Korea; Landstuhl Regional Medical Center in Germany, and Kadena Medical Facility at Kadena air base in Japan.