1952, with a graduation date of 1 March 1952. Its duration was 59 days. At the time, Ranger training was voluntary. In 1966, a panel headed by General Ralph E. Haines Jr. recommended making Ranger training mandatory for all Regular Army officers upon commissioning. On 16 August 1966, the Chief of Staff of the Army, General Harold K. Johnson, directed it so. This policy was implemented in July 1967. It was rescinded on 21 June 1972 by General William Westmoreland. Once again, Ranger training was voluntary. In August 1987, the Ranger Department was split from the Infantry School and the Ranger Training Brigade was established. The Ranger Companies that made up the Ranger Department became the current training units—the 4th, 5th and 6th Ranger Training Battalions. Desert Phase was added in 1983 and the length of the Ranger course was extended to 65 days. The duration was again expanded in October 1991 to 68 days, concurrently with the reshuffling of the Desert phase from the last phase to the second. The 7th Ranger Training Battalion was added to administer this phase. The most recent duration change to Ranger School occurred in May 1995, when the Desert Phase was removed from the Ranger course. Ranger School was reduced to its current 61-day length of training, at 19.6 hours of training per day. The Ranger Assessment Phase, the first five days of Ranger School, was added in 1992. In 2015 Ranger School was permanently opened to women. Students Ranger School is open to all Military Occupational Specialties (MOSs) in the U.S. Army, although—as of April 2011—an Army combat exclusion zone still limits some from attending, but this does not include women as women are now allowed to attend the school. Ranger students come from units in the United States Army, Marine Corps, Air Force, Navy, Coast Guard, and from foreign military services. However, the two largest groups of attendees for Ranger School are from the U.S. Army's Infantry Basic Officer Leadership Course (IBOLC), and the 75th Ranger Regiment. Competitions and pre-Ranger courses are typically used to determine attendance. The Marine Corps is only allotted twenty slots for Ranger school each year, while the Air Force is only allotted six. Ranger students typically range in rank from Private First Class to Captain, with lieutenants and specialists making up the largest group. The average age of a student is 23, and the average class