Edward Turner increased the size of the 500 twin to 650cc in order to offer a more powerful machine to American riders to better cope with their longer road trips, and this new machine was christened the Thunderbird. It was revealed in 1949, and was the first 650cc parallel twin.
Three Thunderbirds lapped the banked Montlhery circuit in France for 500 miles, averaging 90 mph, and followed this up with a flying lap timed at over 100mph. They were then ridden back to the Triumph factory in Meriden. It was an outstanding performance, and the motoring press made much of it.
Its praises were also sung in the United States where a California engineer fitted the 650 Thunderbird with a twin carburettor cylinder head designed for GP models. His machine, the Wonderbird, took the motorcycle world speed record in 1955 and held it until 1970.
Marlon Brando played the part of the leader of the The Black Rebels Motorcycle Club in "The Wild Ones". . He rode a Thunderbird T6.
Enormously popular, the T-bird retained its original appearance throughout its decade-long lifespan, whilst undergoing numerous chassis and engine improvements.
Introduced shortly after Triumph was absorbed by the BSA group in 1951, production ended in 1962 - though it still appeared in some catalogues as late as 1964.
Sources include Webbs Auction House NZ