Twenty-seven A3s were built from new, until 1935, with little variation except for a new type of boiler with a "banjo dome", an oval steam collector that was placed on top of the rear boiler ring. The first banjo dome was hidden beneath the casing of Cock o' the North of 1934; it was subsequently used in the A4 streamliners. The last nine A3 Pacifics were constructed with the device in 1935, and it became a standard fitting on all LNER large, wide-firebox boilers that were applied to new locomotives until 1949. It was also applied to replacement boilers on the A3s.