The English Electric Canberra bomber. The last T4 in the RAF , flew its last sortie on 1st Sept this year after 54 years of the type in service. That leaves a number of PR9 Canberras still operational in active service until July 2006, making a total of 55 years in service.
Prototype was first flown in 1949
http://www.rafmarham.co.uk/relations...4-last-flight/
Richard