In contrast to the Mk.4 there were several important changes. The motor was further upgraded from the Magpie III to the new Linnet which offered significantly higher performance and boosted the typical top speed of the missile from Mach 2.4 to 3.2 whilst almost doubling effective range to . The adoption of transistorized circuits in place of the former thermionic valves eliminated the need for cooling the electronics, as well as making the guidance section significantly smaller. This allowed the warhead to be moved from its former position near the tail to the midsection, which also allowed it to grow in size and weight, replacing the former blast-fragmentation type with an expanding-rod system that was significantly deadlier. This also allowed the steering fin actuators to be placed at the rear of the missile, eliminating the pushrods and their associated complexity.