Ranger School
The United States Army Ranger School is an extremely demanding, and prestigious, school in infantry tactics and small unit leadership. A substantial number of the candidates do not complete it, and even completing it may not result in qualifying for the "Ranger Tab" badge.
One does not need to complete Ranger School as a prerequisite for assignment to the 75th Ranger Regiment, and, indeed, most junior soldiers assigned there go through an abbreviated Ranger Indoctrination Program.
It is an important milestone for combat arms officers and noncommissioned officers; United States Military Academy cadets sometimes attempt it in the summer between their junior and senior years. While the majority of places are reserved for combat arms, soldiers from certain combat support branches, such as military intelligence, may go through it, and, if they succeed, obtain considerable credibility with combat soldiers.
Even among combat troops, it both adds skills and confidence to the soldier, and also can resolve doubts about officers thought to be "staff", "politicians", or "intellectuals". GEN David Petraeus was suspect, to some "old Army" officers due to his doctorate from Princeton, but the fact that he was the only man ever to be first in his class at both the Ranger School and Command and General Staff College overcame many doubts.
As demanding as Ranger School may be, it is considered preparation for some of the special operations selection courses, as for Delta Force. United States Army Special Forces selection has some of the physical demands, but also has intense intellectual demands in operating in a simulated behind-the-lines guerilla role.