The first 'Fixed Hospital' was authorised at Kilmainham in Dublin in 1691 and a year later the first 'Marching Hospital'. These, through a process of evolvement became the General and Flying Hospitals.
The General Hospitals continued to evolve through the ages to match the new medical needs of the Army, which in turn was reacting to the technological advances in weaponry and destructive effect on the field of battle.
In the late 19th Century the Flying Hospital had become known as the 'Clearing Hospital'.
As a result of experience gained in the Boer War, the problems associated with the spreading of meagre medical resources along the long lines of communication and the recognised need to review the medical support between the Field Ambulance and the General Hospital acted as the spur to the implementation of the 'Clearing Hospital'. This unit went to war as 2 Clearing Hospital