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Sea Slug

The Seaslug was an early Royal Navy SAM that served in the Falklands War but earned no victory credits. British missiles in the early years of the Cold War had the most fascinating names: Red Shoes, Blue Jay, Firestreak, Bloodhound, Black Knight, Blue Water, Blue Streak, Blue Steel, Sea Cat, and the rather unattractively named naval weapon, Sea Slug. This missile was named, for some reason, after a marine animal sometimes called a sea slug or a sea cucumber, which has a long, tough, muscular body.

In the Falklands War the Royal Navy ships operated a mixture of gun defenses and SAMs (Seacat, Seawolf, Sea Dart, and Seaslug). The British put their first SAM, the Bloodhound, into service in 1958; the Thunderbird in 1960; and the Seaslug in 1962. These first-generation missiles had command guidance systems and were large (about 20 feet in length).

Tthe Seaslug antiaircraft missile complex, which includes three radar stations — detection and target indication, target tracking, and beam guidance radar. The complex's missile is supersonic, two-stage with four side-mounted jettisonablc booster engines. Range is up to 40 km, maximum velocity is 1,030 m/sec, and the ceiling is 20-23 km. It was automatically fed from a magazine below the decks, and is operated and fired from positions within the ship without anyone on duty being in an exposed place.

In 1958, the rôle of the Navy was clearly defined, with three separate commitments: peacetime, limited war and global war. In subsequent years, the re-equipment of the Fleet proceeded apace. This included new ships such as the County class guided missile destroyers, new aircraft such as the Scimitar and Sea Vixen, and new weapons such as Sea Slug.

A decade later, a variety of capabilities were being planned to enable the Royal Navy to counteract the Soviet Navy's cruise missiles. Besides direct engagement of the missile ship, the Royal Navy's counter to cruise missiles would be provided by the Sea Slug surface-to-air missile system and by the new close range Sea Wolf and medium range Sea Dart systems then under development. Electronic countermeasures against this form of attack would also be available.

Tests were carried out with Sea-slug and by 1959 had been exceedingly satisfactory, the results exceeding the expectations. After a final trial in the summer of 1959 the weapon went into production late the year. In the meantime, four guided-missile destroyers of the County class had been ordered and two of these had already been laid down. The County class was single-ended ship carrying Sea Slug aft, so these guided missile destroyers could engage only one target at a time with Sea Slug. Contemporary American and Russian destroyers, were double-ended, so presumably they can engage more than one target at a time. The Mark II Sea Slug was on the "Fife" and "Glamorgan", the last of the guided missile destroyers of the "Devonshire" class.

The 1967 Statement on Defence Estimates included plans to convert H.M. Ships "Devonshire" and "Hampshire" to carry the Seaslug II missile during their extended refits. On 01 May 1968 the Secretary of State for Defence announced that "In view of the progress with our plans for the new Sea Dart destroyers, we have now decided not to convert H.M. ships "Devonshire" and "Hampshire" to carry Sea Slug II. Plans for the conversion of H.M. ships "Kent" and "London" are being considered in the light of the Prime Minister's statement on economic policy in January."

Together with the destroyers which were to carry it, it cost round about £140 million, which is the cost of nearly three Polaris submarines. Seaslug, originally estimated to cost £2½ million, was by 1960 estimated at £40 million. The direct cost of developing the missile and its control and guidance system was £40 million, while the total estimated all-up cost was £70 million, including the ship-borne radar developed by the Admiralty.

In the Seaslug Mk. 1 trials ship, H.M.S. Girdle Ness, the R.N. were provided with a completely centralized, quasi-automatic radar monitoring system, for its day, the mid-1950s, very sophisticated. The sophisticated system failed; the engineering capability could not justify the philosophy; clumsy electro-mechanical switches, poor inter-connection techniques, unreliable thermionic valves and undisciplined circuit design, and escalating cost, all combined to destroy what was in fact a perfectly sound philosophy.

Beam rider missiles use a rearward-facing antenna in the missile to sense the target tracker's signal. By using onboard equipment to determine its position in the target tracking radar (TTR) beam, corrections can be calculated and sent to the control surfaces to keep the missile as nearly as possible in the center of the target tracking radar's beam or scanning axis. Since tracking errors for this system relate directly to target tracking accuracy and the TTR's beamwidth, these systems are generally restricted to short ranges. SAM systems using this type of guidance are the British Seaslug, the US Navy's Talos and Terrier system, and the RBS-70.

Viewed from the most elemental aspects, in beam-rider guidance the missile must be brought within the radar beam before guidance can be established; the radar must rack the target in such a manner that the missile is not lost from the beam; the guidance intelligence must direct the missile correctly within the beam; and the beam-rider guidance system mnust bring the missile to a point where it is possible for the homing system to take over control, if terminal guidance is used.

The simplest method of getting a missile into the radar beam is to use a missile and booster of sufficiently stable flight characteristics that it may be launched into the beam, Unfortunately, the manufacture of missiles and boosters was not of precise character, with the result that considerable dispersion occured during the launching and boost phases of flight. Statistical data were not available on specific missiles in sufficient quantities to provide quotable figures. Missile manufactures indicated a belief that 95 percent of the missiles may be contained within ±5 degrees at the end of the boost period, considering ballistic and booster errors only. An evaluation of the Seaslug gathering problem indicated that ballistic angular errors only might be assessed at ±4 degrees, with 95 percent of the missiles to be contained with this estimated dispersion.

The maintainer was at the end of the line, his task increasing at an ever increasing rate and he was stuck with the errors and omissions of all the rest. An example of the increase in complexity is that the automatic monitoring system for the Sea Dart radar about to be fitted in ships in 1968 had a higher component population than the entire Seaslug radar already fitted; the proportion of monitoring to total components is the same for the two equipments.

The development of R.N. guided missiles and the attendant problems of shipborne missile testing provide a splendid example of the interdependence of technique and philosophy. The Seaslug Mk. 1, Seaslug Mk. 2 and Sea Dart, followed each other in the given chronological order. Sea-dart was a new medium-range surface-to-air guided missile which succeeeded Sea Slug. The immediate R.N. needs and the benefits of A.T.E. (automated test equipment) were appreciated in the very early stages of Seaslug Mk. 1 conception, the R.N. were provided with a highly automated M.T.E. (missile test equipment); this system was fully engineered and fitted, with its automated M.T.E., into four operational ships of the County class.

Meanwhile during the long time scale associated with development, production, ship-building and ship fitting, Seaslug Mk. 2 development was well under way, and this time the agreed M.T.E. policy was a pronounced step backward from automation to an almost entirely manually operated M.T.E. Meanwhile during the time that Seaslug Mk. 2 was being fitted into ships Sea Dart development was well under way, and, because there was no good proven reason for changing the Seaslug Mk. 2 policy, the Sea Dart M.T.E., to be fitted into ships is also almost entirely manually operated.

It is quite possible that the automated M.T.E. philosophy of the Mk. 1 Seaslug was right but the capability of the technique, or "state of the art" current at that time could not justify the decision; for many reasons, some of them totally divorced from automation as such, the faith of the R.N. in A.T.E. was further reduced, hence the choice, with perfectly valid, rational reasons, of manual M.T.E. for Seaslug Mk. 2 and Sea Dart.

The probable ironic final sequel, again resulting from the interaction of technique capability and philosophy, is, that although the A.T.E. techniques have by 1968 advanced to the point where a perfectly satisfactory automated M.T.E. could be produced, missile design has also advanced to the point where shipborne M.T.E. could probably be dispensed with altogether.

Sea Slug was an excellent weapon, though rather large, which is possibly why it was not taken up by other navies. Is any more development work being done on this weapon? It seems that the American Tartar, which was not as good a weapon but is smaller, had a much larger order from foreign countries.

"Devonshires", guided missile destroyers, were armed with one Sea Slug and the Type 42 with one Sea Dart. Sea Slug and Sea Dart were surfact-to-air missiles with a surface-to-surface capability. Their range was a secret, but it was well known that the range of Sea Slug does not exceed 30 miles at the outside and that that of Sea Dart does not exceed 40 miles. What good are those weapons against a ship armed with a surface-to-surface missile with a range of over 200 miles?

By 1980 three County class light cruisers had been scrapped. HMS "Kent" and HMS "Hampshire" had been scrapped and HMS "Devonshire" was on the list. That was done by the previous Administration. The DLGs were let go because they were armed with obsolete sea-to-air missiles, namely, Sea Slug 1. They could have undertaken other functions; their antisubmarine warfare capability could have been improved.

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Page last modified: 14-05-2013 19:27:15 ZULU