Sea Dart -the Vital Statistics.

	Mod 0
Attack Speed	1370-2740mph
Maximum Range	80,000yards
Maximum Altitude	70,000ft
Fuze Type	Non-coherent Pulse Range Gate
Warhead Type	Continuous Rod
Explosive content	13Kg
Sustainer motor	Odin ramjet
Booster motor	Chow
Missile Length	4.4m
Missile Diameter	0.420m
Wing Span	0.9m
Weight	544Kg
Cost	£41,000

When Sea Dart entered service there seemed to be confusion over the warhead type, there being statements that it was a fragmentation round, or an 'externally grooved fragmentation warhead', and one former colleague who worked on the missile confidentially told me that it was a continuous rod warhead but made of Terylene rather than steel. I have been able to establish that Sea Dart carried the K27A1 continuous rod warhead with conventional steel rods. Oddly enough the warhead did contain Terylene, as a binder for the TNT/RDX mix.

The Sea Dart requirement (originally known as NIGS and SIGS -SIG36) was defined by NSR 6502 Issue 4, with the need to equip the Type 82 destroyers which would be entering service in 1971.
The system was to be readily adaptable for use with various 2D and 3D surveillance radars, and the Royal Navy's intent was to use the Anglo-Dutch Type 988 (Broomstick) set.
The Type 909 was to be used for guidance of the missile, and also for gunnery control (GSA 1) and for control of MATCH*.
Provision was to be made for a visual sight.
The AA target priority laid down was:
1 -Low altitude attack by aircraft, air launched missiles agains own ship down to 15m altitude.
2 -Low altitude aircraft or 'aircraft equivalent' missiles against ships in company.
3 -Medium or high altitude aircraft against own or other ships up to 20,000metres altitude.
4 -Attacks by 'other missiles' against own ship.

Examples of missile targets: 'Aircraft equivalent' -Regulus, Kipper.
Other missiles -Subroc, longer range versions of Bullpup, AS 30.
Sea Dart's maximum speed was to change linearly with height, M1.1 at 15m, M1.5 at 50m, then M2 at 10,000m and M3 at 20,000 metres.
It was required to engage targets at angles of dive of up to 70 degrees and at horizontal crossing angles of at least 70 degrees. "Any additional performance which is obtainable against receding targets will be considered a bonus." As far as I know, HMS Gloucester's successful engagement of a Silkworm fired at USS Missouri is the only known such interception.
Low altitude attacks may involve a 'vertical pull-up' not exceeding 4g which will not start within 8,000 metres. A continuous lateral weave will not exceed 1g with a period of 20 seconds.

Maximum length: 14' 4"
Span: as small as possible but must be able to pass through a 4' square aperture.
Weight: not to exceed 1,200 pounds.
Liquid fuels liable to spontaneous ignition are to be avoided.
Not les than 85% of missiles loaded onto the launcher should achieve normal flight.
Not less than 95% of missiles should remain serviceable after six month's stowage [on board ship].
Routine overhaul not required within 5 years of manufacture.

Telemetry requirements: It is acceptable for the telemetry sender to replace the warhead. Either a transmitter for use with the UHF version of the American miss-distance measuring equipment (AN/USQ-11A) or a tag to use with the UK Radio-active miss distance indicator (being developed) is required.

Surface targets: a range of at least 20,000 metres against a destroyer, a direct hit as near to the waterline as possible and penetration being achieved on destroyers and typical medium-sized merchant ships. Additional damage by near misses to 'soft' upper deck targets such as radar aerials is highly desirable.

The system must be able to cope with the following accelerations:

	Up	Down	Sideways
Director level	15g	10g	8g
Launcher	25g	15g	10g
Magazine	25g	15g	10g

The warhead selected is the K27A1 and is of the continuous rod type. It contains a standard 60/40 mix of RDX and TNT with addition of Terylene (0.25% of the total) and the liner/lens is polythene.
Total weight of the warhead is 58 lbs, the rod velocity after break-out from the missile skin is 3,400 feet per second and its 90/90 radius is 27 feet.

*Match was an anti-submarine weapon which eventually turned into the Wasp helicopter.

In 1969 Hawker Siddley Dynamics (HSD) proposed an anti-ship sea-skimming variant; the ramjet sustainer would have been fuelled with Shelldyne instead of kerosene. Shelldyne was significantly denser and would have given the missile a significantly greater range, approximately 37km (the same range as the missile in the conventional 'up and over' trajectory) as opposed to 24km. The missile would have used the same CW radio altimeter as proposed for Seaslug; this altimeter was fitted to the Phantoms built for the FAA. It was intended to fit a semi-armour-piercing warhead immediately behind the nosecone, and move the electronics back into the space normally used by the radio fuze.

Sources: National Archives DEFE 13/558, ADM 333/16 /19 & /20

A short report on a surface-to-surface trial shoot.

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Comments to: seaslug@littlewars.org.uk.
Last updated: 30^th September 2020.
Copyright SR Jenkins, January 2019