Washington announced this week it was sending up to 275 troops to Iraq. We don’t know what units have gone to the imperiled nation, but we have some clues.

The Pentagon and U.S. Central Command—which overseas military operations in the Middle East—have both declined to specify who is deploying to Iraq. But reading official press releases, we know the troops came from American bases in the region.

Other reports suggest that the contingent includes both Marines and soldiers. Each of these services has forces in the area that are on call to protect Americans.

The jarheads are likely from a Fleet Antiterrorism Security Team. CENTCOM has its own FAST company—members of which are seen in the picture below—but there are other detachments available as well.

These units have around 50 personnel and are designed to provide backup to American military and diplomatic posts around the world.