The Seaslug Mark 2 was based on the aborted Blue Slug programme to develop an anti-ship missile using the Seaslug missile and guidance system. The project was cancelled in favour of the "Green Cheese" missile, a tactical nuclear anti-ship weapon, but other project developments were incorporated into what became the Mark 2. It had improved low altitude performance and a limited anti-ship capability and entered service in 1971. The Mark 2 utilized an improved beam-riding guidance system. and solid-state electronics. It was powered by the "Deerhound" sustainer motor, with "Retriever" boosters. Control was by a modified Type 901M radar and it had an improved infra-red proximity fuze and a continuous-rod warhead with a smaller, , explosive charge (RDX-TNT) and an unfold diameter of about 70 feet (10 mm steel rods were used)