The A24 design specification had originally been constrained by the available tank engines of the time, delivering only 300 hp and limiting the weight. The evolution to A27M increased the weight slightly, but fitting a 600 hp engine almost doubled the power-to-weight ratio and created a very fast tank. This was combined with the Merrit-Brown gearbox that allowed the tank to steer while still powering both tracks, allowing it to maintain speed while manoeuvring, while tanks like the Sherman or T-34 lost power while turning and necessarily slowed down.