In April 1951, an initial production order for 25 Valiant B.1 (Bomber Mark 1) aircraft was placed by the Ministry of Supply on behalf of the RAF. The timing of this order was key to establishing production quickly. Due to shortages of steel and other materials while setting up an assembly line at Brooklands, substantial portions of the production jigs for the Valiant were made from concrete. The first five Valiants produced were completed to a pre-production standard, the first being WP199. On 21 December 1953, the production aircraft conducted its first flight; this had again occurred within the schedule that Edwards had promised.