  :Both Tallboy and Grand Slam were intended to be dropped from an optimum height of 40,000ft but until the Victor there was no bomber capable of carrying either bomb to that height.  :When the Lancaster was used, a reduced dropping terminal velocity/penetrating power was accepted as this was still more than adequate. Wallis was hoping to be allowed to build his Victory Bomber to carry the Grand Slam up to 40,000ft but the design was not accepted and so it was never built.