An intended A/S version, the Type 11 class (see Type system of the Royal Navy), was cancelled due to the low 24-knot top speed being insufficient for accompanying fast carrier task forces, particularly with HMS "Eagle", the flagship, commissioned in 1951. However, in practice, frigates and destroyers moving at more than 25 knots create turbulence which blinds their own sonars and can only engage fast-moving subs by using a helicopter with its own sonar. Thus the Type 41s were still fitted with the best late-1950s RN sonars, types 170 and 174 (which remained a good passive sonar into the 1970s), but were equipped with only a minimal A/S mortar battery.