The US Army's next generation Chinook, the CH-47D, entered service in 1982. Improvements from the CH-47C included upgraded engines, fibreglass rotor blades, a redesigned cockpit to reduce pilot workload, redundant and improved electrical systems, an advanced flight control system (FCS) and improved avionics. The RAF returned their original HC1s to Boeing for remanufacture to CH-47D standard, the first of which returned to the UK in 1993. Three additional HC.2s were ordered with delivery beginning in 1995.
Helicopters - Parked
Six further Chinooks were ordered in 1995 as Chinook HC2As. The main difference between these and the standard HC2 was the strengthening of the front fuselage to allow the fitting of an aerial refueling probe in future.
Links: en.wikipedia.org, www.airliners.net