1901-1966, shipbuilders; marine engineers, Chiswick, London and Woolston, Southampton, England

John I. Thornycroft and Co Ltd was founded in 1864 by John Isaac Thornycroft, a naval engineer. He commenced building steam driven launches at Chiswick, London with his partner John Donaldson in 1872. In 1896 John Isaac Thornycroft built his first steam lorry. The company was a manufacturer of commercial vehicles at Basingstoke from 1896 to 1960. In 1899 John Donaldson died.

The company became public in 1901, in order to acquire the business of builders of torpedo boats and to bring in more capital and was registered on the 22nd May. The funds were chiefly provided by William Beardmore who hoped to make the shipbuilding firm a tied customer for his iron and steel and to expand the infant Scottish motor industry but these hopes were not fulfilled.

In 1902 they built their first petrol-engine vehicle and in June 1904 the company relocated to Woolston, Southampton, where it acquired the Mordey, Carney & Company shipyard, the move made necessary by the increasing size of torpedo boats and destroyers. By 1904 Beardmore had lost interest in Thornycroft's company and resigned as chairman in 1907. From then on the firm was largely run by Thornycroft's eldest son, John Edward, who oversaw the removal of the shipyard from Chiswick to Woolston. The Chiswick yard closed completely in 1909.

In 1907 the vehicle side of the company completed its move into internal combustion engine power. John Isaac Thornycroft died in June 1928. In 1948 the vehicle making side of the company was put into a wholly-owned subsidiary, Transport Equipment (Thornycroft) Ltd, to prevent confusion with the shipbuilding company.

In 1966 the company taken over by Vosper and Co and called Vosper Thornycroft by 1970.