 Most United States Air Force (USAF) Hercules aircraft were fitted with Explosion Suppressant Foam (ESF) since the Vietnam war.Similarly, the Royal Australian Air Force (RAAF) Hercules aircraft were fitted with the foam system in 2004.Pilots from these air forces serving on exchange had expressed grave concerns about the safety of RAF Hercules, as did some RAF pilots, such as Squadron Leader Chris Seal who had written a memo in 2002 detailing lessons learned in Afghanistan and the necessity to fit ESF in all Hercules aircraft.