The GWR's General Manager, Sir Felix Pole, was anxious for a new design that would once again enable the company to claim to run the most powerful locomotive. Pole agreed to allow Collett to explore a design for a "Super-Castle", subject to getting the tractive effort above . By 1927 a series of bridge renewals had taken place on the Great Western mainlines. This was coupled with the widely known (but as yet unpublished) findings of the Bridge Stress Committee, which gave engineers a better scientific understanding of the impact of hammer blow, and enabled the GWR Civil Engineer to agree to raise the maximum allowable axle-loading to for the new ‘Super Castle’ class.