Between 2003 and 2006, a new category of forces was created, principally to improve the flexibility and reach of land forces. The structure incorporated six "NATO Rapid Deployable Corps headquarters." Formed from October 2003, the NATO Rapidly Deployable Corps are designated High Readiness Forces (HRF), designed to be able to react on short notice. Although these forces cannot deploy on five days warning like the NATO Response Force (NRF), they have a longer sustainment capability in combat than the NRF, which is limited to 30 days.