The background to Seaslug.

Seaslug's background can be traced back to the British wartime 'Brakemine' project which started in 1943, when two Cossor engineers (LH Bedford and L Jofeh) worked out a practical radar guidance system during an overnight train journey. Their resulting report reached the GOC of Anti-Aircraft Command (General FA Pile) at about the same time as a paper written by Captain HB Sedgefield of REME. Pile convened a meeting to discuss this on 27 April 1943, and approval was given for Cossor to run a project to investigate this -at their own expense! This was an experimental solid-fuelled missile about 2 metres long with an 840mm wingspan, fired from a modified 3.7" AA gun mounting.  By the contract end in 1947 Cossor had solved the guidance problems of beam riding and perfected the necessary techniques of triggering high-speed photography etc., which was of value to all future missile projects; the project appeared to have been cancelled just as it appeared to be showing results. The truth, however, was different. The project was merged with Ben to become LOP/GAP -RTV1 (Liquid Oxygen Petrol/Guided Anti-aircraft Projectile -Rocket Test Vehicle 1) which was used to prove concepts.

Armstrong Whitworth Aircraft (AWA), Sperry Gyroscope and the General Electric Co (GEC) collaborated to work on the Navy's Project 502 to establish if a guided missile was a practical/workable proposition. A great deal of work was done using Shorts' General Purpose Test Vehicle (GPV) at Woomera to assess the guidance system. A GPV can be seen behind the Seaslug missile here, it is worth noting it also has the forward mounted boost motors. The Project 502 team went on to design Seaslug and work on Seaslug started in 1949 with the missile airframe being designed by AWA (which became Whitworth Gloster, then Hawker Siddeley Dynamics and finally part of British Aerospace Dynamics), the guidance package by Sperry and the guidance radar by GEC. There are some reports of the name Seaslug appearing as early as 1946.

RTV1 was used to prove both guidance and fuzing,with the first successful interception occuring in 1954. At this stage it was believed that it would take too long to design a reliable solid-fuel motor that could provide thrust for long enough (35-40 seconds) so the team concentrated on liquid fuelled engines; Liquid oxygen & petrol, HTP & kerosene and Nitric Acid (RFNA) & kerosene. The Navy opted for the last combination as it was regarded as the least unwelcome fuel combination on board a ship. As it happened the rest of the programme suffered delays which gave IMI Summerfield enough time to develop an adequate motor -Foxhound- which became available in 1956.
HMS Girdle Ness' trials started in 1956, so apart from the first few they would have used Foxhound solid-fuel motors. After a prolonged test period over test 250 missiles were fired, most at the British test range at Aberporth from fixed launchers as well as HMS Girdleness; others were fired in the Mediterranean and at Woomera.
Seaslug finally entered service in November 1962 when the system was accepted on board HMS Devonshire. The Mk1 missile was only really capable of engaging trans-sonic targets and its electronics were comprised of thermionic valves (or tubes).
With Seaslug's entry into service the Project 502 team continued to work on improving the missile with the Mk2 version -featuring solid-state electronics, a higher ceiling and longer range- entering service in 1971. The Mk2 missile was supersonic and used discrete solid-state components.

The story does not end here, however. In the late 1960s the Project 502 team proposed an 'improved Seaslug' for the Navy's Small Ship Integrated System (SIGS) in competion with Bristol Aeroplane GW Department. Bristol's submission had too short a range to be acceptable so they looked to Bristol Engines for a better power source which led to a proposal called RP25. The Navy approved of the design but wanted the Project 502 team to have design authority. This design turned into a relatively small, sleek missile to which the Ministry of Aviation allocated the designation CF299 -SeaDart!

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Last updated: 24th September 2016.

Copyright SR Jenkins, February 2012.