Ploughing through the documents in The National Archives I have obtained further information on Seaslug firings from HMS Glamorgan's log. Note: all times are 'Zulu', ie GMT; subtract 3 hours for local time.
26th May: 02:30 to 04:05, engaged shore targets with 4.5" guns.
26th May: 03:50 Seaslug launched.
28th May: 02:30 Seaslug launched.
28th May: 02:45 to 03:50, engaged shore targets with 4.5" guns.
28th May: 03:10 Seaslug launched.
30th May: 02:00 to 03:45, engaged shore targets and on Port Stanley airfield with 4.5" guns.
30th May: 02:30 Seaslug launched.
12th June: 01:47 to 03:00, engaged shore targets with 4.5" guns,
12th June: 06:37 Hit by Exocet missile.
The MM38 Exocet missile was fired from an extemporised launcher mounted on a trailer with a laptop computer feeding the expected radar data; the launch was seen by Glamorgan's crew but not recognised for what it was. Shortly afterwards, however, the missile's trail was seen and at about the same time it was detected electronically; it is not clear whether this done by the 992Q radar or by the detection of transmissions by the Exocet's homing head. The helm was put hard over to put the ship stern-on to the approaching missile so as to present the smallest target; the County Class were very manoeuvrable ships and during tight turns exhibited a large degree of heel [See this image of Glamorgan turning hard taken a few years later]. This turn undoubtedly helped the ship survive, the Exocet struck before the turn had been completed and instead of striking Glamorgan's hull side it slid along the deck alongside the hangar before the warhead detonated. [This picture shows the hole in Glamorgan's deck and the missile's 'skid mark']. The downward curve of the edges show that the explosion occurred above the deck. The port Seacat launcher (previously damaged in an air attack) was blown off its mount, the hangar and the Wessex helicopter within it were burnt out. Tragically the ten-strong damage control party had formed up in their station, the Junior Rates' mess; this was directly below the exploding warhead and they were all killed. It is a tribute to Glamorgan's crew that not only did the ship survive the Exocet attack but the damage was confined to the hangar area (including the Seaslug Type 901 radar) and the Mess Deck.
Sources: TNA ADM531/90359 & 90360.
An engineer who examined the damage the following day considered that a major factor in the ship's survival was the preparedness of the damage control teams and the large on-board stock of AFFF additive for fire fighting. The RN damage control school certainly used the incident as an example of how to do it right.