Seaslug Mk2 alternative fuzing.

In May 1971 an investigation was commenced to improve the fuzing of the Mk 2 missile, as it was believed that the passive Infra Red fuze might trigger too soon or too late under some circumstances. The existing fuze was the GW17 which used a narrow-band IR detectors centred on 4.3 microns (4300 nm) with a wide-band sun-guard channel centred on 1 micron (1000 nm). Any source detected by both channels was disregarded, but one that appeared on the 4300 nm channel alone would cause the warhead to be detonated. A later refinement fitted to all Mk2 missiles was the Fuze Segment Selector Unit. This switched out segments of the fuze likely to be triggered by exhaust plumes or reflections of hot sources from the surface of the sea. Fuzes fitted with the FSSU were designated SW42.

Four alternative fuzes were considered:1) A non-coherent conical look-angle radar fuze based on the Pranger fuze fitted to Sea Dart.
2) A Pulse Doppler fuze being developed for Sea Wolf.
3) An electrostactic capacitance fuze based on that fitted to Blowpipe.
4) A new passive Infra Red fuze being developed by EMI.

The Pulse Doppler worked on two bands, 1-45KHz and 45-90KHz and used a guard channel to perform range retraction in order to prevent premature firing from sea reflections. The development cost for Sea Wolf was £12,092 over 5 years, and £621 per fuze; the cost to develop this fuze for Seaslug was estimated at £1261 over four years and £1,400 per fuze.
It was decided not to pursue any development of the capacitance fuze as it was believed that the boost motors would coat the missile with aluminium compounds which would be removed during the missile´s flight and so change the missile´s electrostatic capacitance.
The final option was based around the new VX 8568 sensor developed by Mullard which had a sensitivity of 0.4µW/cm2 and only needed cooling to -40°C as opposed to the GW17´s 77°K (-196°C). Development cost was estimated as £773,550 with a cost of £1,150 per fuze plus £250 for the Mullard detectors. After due consideration this option was selected, but in the event none of these options were pursued and Seaslug Mk2 retained the SW42 fuze for the remainder of its service.

Source: TNA -AVIA6/24114.

This page copyright SR Jenkins February 2015; reproduction without prior approval is prohibited.
Page last updated: 24th January 2019.
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