It was designed by G. J. Rackham, an employee of the American firm Yellow Coach from 1922 to 1926, leading him into contact with the Fageol Twin Coach. It was not until a visit to America in the late 1920s that Rackham noted the success of the 1925 Twin Coach which had won large sales to American operators. The result was Rackham returned to Southall (AEC's Works) with the idea of implementing American practice of side-mounted engines in British bus production.