Rangers Lead The Way No Matter What The Conditions

Ranger School is one of the toughest training courses for which a Soldier can volunteer. Army Rangers are experts in leading Soldiers on difficult missions— and to do this they need rigorous training. For over two months, Ranger students train to exhaustion, pushing the limits of their minds and bodies.
The purpose of the U.S. Army's Ranger Course is to prepare these Army volunteers — both Officers and enlisted
Soldiers — in combat arms related functional skills. The Rangers' primary mission is to engage in close combat and direct-fire battles. There are three distinct phases of Ranger School that require Soldiers to make quick decisions in adverse situations these phases are called 'crawl,' 'walk' and 'run.'

Schedule Of Phases

Crawl Phase

The Crawl Phase lasts 20 days. It's designed to assess and develop the necessary physical and mental skills to complete combat missions and the remainder of Ranger School successfully. If a student is not in top physical condition when he reports to the Ranger School, he will have extreme difficulty keeping up with the fast pace of Ranger training, especially the initial phase.

Walk Phase

The Walk Phase takes place in the mountains and lasts 21 days. During this phase, students receive instruction on military mountaineering tasks as well as techniques for employing squads and platoons for continuous combat patrol operations in a mountainous environment. They further develop their ability to command and control a platoon-sized patrol through planning, preparing and executing a variety of combat patrol missions.

Run Phase

The Run Phase of Ranger School continues to develop the Ranger students' combat arms functional skills. They must be capable of operating effectively under conditions of extreme mental and physical stress. This is accomplished through exercises in extended platoon-level patrol operations in a swamp environment. Run Phase training further develops the students' ability to lead small units on airborne, air assault, small boat, ship-to-shore, and dismounted combat patrol operations in a low intensity combat environment against a well-trained, sophisticated enemy.

 http://www.goarmy.com/soldier-life/being-a-soldier/ongoing-training/specialized-schools/ranger-school.html