The RAF, USAF and Luftwaffe undertook lengthy evaluation of the Kestrel with NATO funding of the 9 evaluation airframes. The USAF kept hold of 6 of the planes, so it was a bit of a surprise when the US Marine Corps not the Air Force became the first export customer for the Harrier. The desire of the USMC to 'buy American' led to the establishment of the joint venture between BAE and McDonnell Douglas in St Louis to build the aircraft and initiate a technology transfer over the Atlantic. The so called AV-8A had some minor modifications the the avionics (HUD, IFF) to make it more compatible with USMC operations, and by the time it was ordered, Rolls Royce had squeezed 5% more power out of the pegasus.