What is the Islamic Revolutionary Guard Corps?

The Islamic Revolutionary Guard Corps was established 40 years ago to defend Iran's Islamic system. It's estimated that the Revolutionary Guard has over 150,000 active personnel, including ground, navy and air forces. It also oversees Iran's strategic weapons, and is considered the country's dominant military force. The Revolutionary Guard is tasked with patrolling the Strait of Hormuz, where 20 percent of the world's oil supply passes through.