Following reports of Iran firing missiles at an Iraqi air base housing US troops, the website for the U.S. Selective Service System went down.

The Selective Service System is an independent agency of the United States government that maintains information on those who could be drafted.

First, in the event that a national emergency necessitates a draft, Congress and the President would need to pass official legislation to authorize a draft.

The draft has not been used since the Vietnam War in the 1970s.

According to the Selective Service System, nearly all men in the country between the ages of 18 and 25 must register with the agency.

That includes “U.S. born and naturalized citizens, parolees, undocumented immigrants, legal permanent residents, asylum seekers, refugees, and all males with visas of any kind which expired more than 30 days ago.”

Young men in hospitals or mental institutions do not have to register while they’re committed, but they must within 30 days of their release.

Women are not required to register.

Registration is not an automatic sign up for the military, but simply adds you to a database of potential recruits who could be called upon during a crisis.

If a draft were enacted, men would be called to serve in a lottery system based on their birth year and a random number assigned to them. Then they would be evaluated for “mental, physical, and moral fitness” before joining the Armed Forces.

This story will be updated as soon as the Selective Service System website is up and running again.