The National Motor Museum Trust

Early in 1957, Triumph announced a new machine with a twin-cylinder engine that would revive their interest in the 350cc class. The model was called the Twenty-One in celebration of Triumph Engineering Company's 21st birthday. The most striking feature of the new bike was its styling. Inevitably, the rear enclosure, reminiscent of an old-fashioned hip bath, became known as the bathtub.

A year after introduction, the 350 was given the name 3TA. In 1962 The Motor Cycle magazine road tested one example over 900 miles (1,448.41 kilometres). They reported it to be quick and nimble with good brakes, minimal vibration and a fuel consumption of 66mpg. Production of the 3TA ceased in 1966.