Staff Writer (Updated: 4/25/2016):
The Sentinel was born from the Airborne Stand-Off Radar (ASTOR) program of the British Army to which the quick coalition success in the 1991 Persian Gulf War furthered defined the need for a dedicated requirement. The war proved the value of Synthetic Aperture Radar (SAR) as well as Ground Moving Target Indicator (GMTI) when tracking and engaging ground-based foes. Such services were largely supplied by the United States which led the UK to pursue its own stand-alone solution. Prior to the war in 1984, a Britten-Norman BN-2T Islander was outfitted with mission equipment though a dedicated, purpose-built platform was still sought, funding then finally allotted to similarly modify a Bombardier (Canada) Global Express business jet by way of Raytheon equipment. The MoD secured the program - to take on the same of "Sentinel" - in 1993. The end-product would encompass a land and air combination of assets to appropriately fulfill the battlefield role.
The original civilian-minded Global Express business jet program was launched on December 20th, 1993 and went airborne for the first time on October 13th, 1996. The first foreign customer became Malaysia in July of 1999.
The official UK defense procurement contract was awarded in December of 1999. After several years in development which included testing of Rolls-Royce engines and new fuselage additions, an initial prototype recorded its first flight in August of 2001. A production-quality airframe then took to the skies on May 26th, 2004 and completed a flight lasting over four hours - proving the design and its mission suites sound (as well as its new aerodynamic layout). The modified Bombardier aircraft was adopted into RAF service as the "Sentinel R1" and delivered to 5(AC) Squadron ("Army Cooperation") at RAF Waddington - five total airframes were procured in addition to eight mobile ground stations (MGS). While initially expected to have been formally introduced in 2005 delays to the Sentinel program ensured an introduction in 2008.
As can be expected, the Sentinel retains the same basic shape and configuration of the original Bombardier Global Express jet. The design includes a well-streamlined, cylindrical fuselage with the cockpit held well-forward. The fuselage sports a noticeably pointed nose cone at front and tapers to the rear. Wings are low-mounted along the fuselage sides and are capped by winglets for additional stability. The engines are mounted in individual nacelles on short wingstubs just ahead of the tail unit. The empennage itself consists of a single vertical tail fin while horizontal planes are added to the fin to create a "Tee" style configuration. All wing surfaces (main assemblies and tail) are swept for maximum aerodynamic efficiency. The undercarriage is wholly retractable and fits a pair of double-tired main legs at center mass along with a double-tired nose leg under the flight deck. The Sentinel is, however, clearly identified from its civilian-minded breed by the inclusion of a dorsal SATCOM fuselage fairing just aft of the cockpit and an oblong, 15-foot long ventral radome structure housing the applicable mission equipment. Additionally, ventral strakes are noted under the empennage.