Also called the armed forces, the military is a professional organization authorized by a country to use deadly weapons and force. The main role of the military is to defend the country and its citizens. The military may also help defend one or more countries in a war, provide aid in times of crisis, or protect the government from domestic threats

In the United States, there are five branches of military service: Army, Navy, Air Force, Marine Corps, and Coast Guard. The first four of these branches are organized as part of the Department of Defense; the U.S. Coast Guard is part of the Department of Homeland Security. As dictated by the U.S. Constitution, the president of the United States is the commander in chief of the military. This means the president is the top leader of all four branches.

There are different categories of military service. Active duty personnel are full-time soldiers and sailors. There are currently more than 1.29 million men and women in active service in the U.S. military, which is less than 0.5 percent of the U.S. population. The army is the largest branch, with more than 470,000 active duty personnel. The Navy and Air Force each has over 320,000 active duty personnel, and there are more than 180,000 Marines.

Recruits must be a U.S. citizen or resident alien; be at least 17 years of age (17-year old applicants require parental consent); pass a physical exam; and (with a few exceptions) have a high school diploma. Officers—who are trained to be the leaders and supervisors of enlisted personnel—must also have a bachelor’s degree from college.

Each branch of the military also has reserve personnel. The National Guard is organized and controlled by the states and is often used to assist in disaster situations or state emergencies. Reserve and National Guard personnel typically work a civilian (non-military) job, but they are trained to be prepared to be called to full-time active military duty if the country is in need.

The United States currently has an all-volunteer military force. However, all male U.S. citizens are required to register for the draft when they turn 18. A draft is a mandatory enrollment of individuals into the military that can be used in times of war. The nation’s first military draft began in 1940 and continued during times of both war and peace until 1973.

Both men and women serve in all branches. When the draft ended, women represented just two percent of the enlisted forces, but today, women account for roughly 16 percent of enlisted personnel and 18 percent of officers. The Navy has the highest percentage of women; almost 25 percent of active duty personnel in the Navy are women.

Today, the U.S. military maintains almost 800 military bases in more than 70 countries. Most of the troops are in Asia and Europe. The number and location both change in response to threats. In addition, there are more than 420 military installations in the 50 states, District of Columbia, Guam, and Puerto Rico. California is home to more military installations than any other state.