The C-130 Hercules is a four-engine turboprop cargo aircraft and the main tactical airlifter for many military forces worldwide. Over 40 models and variants of the Hercules serve with more than 50 nations. In December 2006 the C-130 became the fourth aircraft (after the English Electric Canberra in May 2001, B-52 Stratofortress in January 2005 and the Tupolev Tu-95 in January 2006) to mark 50 years of continuous use with its original primary customer, the United States Air Force (USAF). The C-130 is capable of short takeoffs and landings from unprepared runways. The C-130 was originally designed as a troop, medical evacuation and cargo transport aircraft. The versatile airframe has found uses in a variety of other roles, including as a gunship, and for airborne assault, search and rescue, scientific research support, weather reconnaissance, aerial refuelling and aerial firefighting. The C-130H model has updated Allison T56-A-15 turboprops, a redesigned outer wing, updated avionics and other minor improvements. Later H models had a new, fatigue-life-improved, center wing that was retro-fitted to many earlier H-models. The H model remains in widespread use with the US Air Force (USAF) and many foreign air forces. Initial deliveries began in 1964 (to the RNZAF), remaining in production until 1996. An improved C-130H was introduced in 1974.