The U.S. Department of Defense (DoD) classifies unmanned aerial systems (UAS) into "Groups" according to their size and capability, a joint system that replaced the service branches' separate categorization schemes in 2011.[1][2][3]
The "Group" system has five categories, whose capabilities increase with the number.[4]
From about 2004 to 2011,[4][5] U.S. military planners used various "Tier Systems" to designate the various individual aircraft elements in an overall plan for integrated operations.[6] The Tiers do not refer to specific models of aircraft, but rather roles the aircraft would fill. The U.S. Air Force, U.S. Marine Corps, and U.S. Army each have their own tier system.
Tier II+: High altitude, long endurance conventional UAV (or HALE UAV). Altitude: 60,000 to 65,000 feet (19,800 m), less than 300 knots (560 km/h) airspeed, 3,000-nautical-mile (6,000 km) radius, 24‑hour time-on-station capability. Complementary to the Tier III- aircraft. Role currently filled by the RQ-4 Global Hawk.
Tier III-: High altitude, long endurance low-observable UAV. Same parameters as, and complementary to, the Tier II+ aircraft. The RQ-3 DarkStar was originally intended to fulfill this role before it was "terminated".[9][10] Role now filled by RQ-170 Sentinel.
Tier III: For two decades, the role of medium range tactical UAV was filled by the Pioneer UAV. In July 2007, the Marine Corps announced its intention to retire the aging Pioneer fleet and transition to the RQ-7 Shadow tactical unmanned aircraft system by AAI Corporation. The first Marine Shadow systems have already been delivered, and training for their respective Marine Corps units is underway.[5][13]
Role currently filled by the AAI RQ-7 Shadow, although USMC planners do not view this aircraft as meeting future Tier III requirements.[14]
Tier II: Short Range Tactical UAV. Role filled by the RQ-7A/B Shadow 200.
Tier III: Medium Range Tactical UAV. Role formerly filled by the MQ-5A/B Hunter and IGNAT/IGNAT-ER, but has transitioned to the Extended Range Multi-Purpose (ERMP) MQ-1C Gray Eagle.