Seaslug Myths and Legends.

Seaslug MK1 had a liquid fuelled sustainer.

As explained elsewhere on this website, initially Seaslug was to have had a liquid-fuelled sustainer; the Shorts' GPV that was used for a lot of the testing and proving work for Seaslug certainly did.  By the time that other design issues had been resolved, IMI had been able to build large solid-fuel rocket motors which were reliable enough to use in missiles, and the Foxhound motor was used for the Mk1 missile.  Although HMS Girdleness was fitted for liquid fuelled missiles (a high-pressure high-volume drencher spray system) I have found no evidence of her firing one.

The Mk2 missile always broke up.

During the initial trials of the Mk2 missile there were issues with the boost motors exploding or breaking up on separation.  However, these problems were resolved -that is what trials are for, and I am aware of only one incident of this nature after the Mk2 missile had entered service.  All trial ranges have safety boundaries and missiles (as well as the drone targets) could not be allowed to cross these, so they were fitted with self-destruct systems called Break-Up-Units to ensure that they could be destroyed before this happened. Typically each firing report of a telemetry missile (which did not have a warhead) would contain the phrase '...the missile was broken up at...' to confirm that the Break-Up-Unit had done its job.

Seaslug Mk2 was never accepted into service.

I spent seven years working on Seaslug in a Naval Armament Depot issuing missiles and spares to the County Class Destroyers.  There were about 60 staff in the Depot who were involved with Seaslug and apart from my office there was the missile test house, two magazines containing missiles, two storehouses for explosive components, a whole underground store at RNAD Dean Hill for rocket motors, and several storehouses for non-explosive components, test equipment and containers.  The other Depot that handled Seaslug would have had the same amount of staff and buildings if not more.  I don't believe that the MOD would have gone to all this expense and use of Depot facilities if they hadn't accepted the missile into service.  Certainly there was no hint of Seaslug not being operational at that time, and the earliest mention of it is in the article on HMS Girdleness (which was only involved with the Mk1 missile) in Warship 2007.

The final version of Seaslug was Semi-Active Radar Homing.

Again this is untrue; Seaslug was a beam-rider to the end.  Unlike Terrier and Talos no attempt was ever made to change to SARH for even the terminal phase. Firstly there wasn't any room in the missile for an aerial or dish, or for any receiver electronics.  Most of the nose was occupied with the infra-red fuze and the safety and arming system.  The only 'empty' space was a rounded cone about 10” high and perhaps 3-4” in diameter.  One of the reasons for choosing beam-riding as the guidance system for Seaslug was that with the receiving antenna at the rear of the missile, it was immune to any jamming from the target.  It also meant that all the data processing was done on board the ship.  As far as I've been able to find out the Project 502 team stuck to beam-riding for the proposed Mk3 version; this was not proceeded with as the Royal Navy preferred the ram-jet powered proposal from Bristol which was given the cover name CF299 -Seadart.

The Chilean Navy converted Seaslug to a tandem boost arrangement.

Yet again untrue.  The boost motors on Seaslug (Gosling H for the Mk1 and Retriever for the Mk2) each generated 12-15 tons of thrust.  Replacing them with a single rocket motor would require at least 20 tons of thrust; there is no way the structure of the missile could absorb that sort of load, it would simply crumple.  The four 'wrap-around' boost motors transferred their thrust to the sustainer motor casing via large castings set into the motor body.  I don't know where this story came from, most people quote the Skomer website.  Unfortunately  Chris hasn't put an e-mail address on so I can't ask him -if you're reading this, Chris, please get in touch!
See this photo for a Seaslug Mk2 being launched by Capitan Prat of the Chilean Navy.  You will see it definitely has its wrap-around boosters 'pulling' it out of the launcher.