Provisionally accepted from Vickers in March 1958, HMS Excalibur was built at a cost of £1 142 000.
Both Explorer and Excalibur were fitted with the latest submarine escape arrangements, including the one-man chamber, and equipped with the most modern escape breathing apparatus for use by the ship's company in the event of an emergency.
Explorer and Excalibur were, not unnaturally, known as the 'blonde' submarines, because of their peroxide fuel, and they served a useful purpose inasmuch as they gave the Royal Navy's anti-submarine forces some valuable practice against fast targets. Their main use, however, was to prove that the HTP system did not represent the way forward for RN submarine development. Indeed, HTP proved difficult to the point of being dangerous, and there was more than one contemporary report of explosions in the two submarines, and at least one instance when the entire crew was forced to stand on the casing to avoid the noxious fumes which had suddenly filled the boat. 'I think the best thing we can do with peroxide is to try to get it adopted by potential enemies', said one RN submariner.
Commander Christopher Russell, who captained HMS Explorer - which was known locally as 'Exploder' because of the huge fireballs from her exhausts when starting up - recalls the dangers of working with HTP:
'The high-test peroxide was a very volatile substance and was carried in special bags outside the pressure hull. Occasionally, there would be a 'whoomph' as one of them exploded. Looking into the engine room, which was unmanned when we were under way, one could see flames dancing along the top of the combustion chamber. We did not look upon her as being dangerous. The crew took the bangs and fires as a matter of course...and fire drill became a very practised affair.'
The development of the hydrogen peroxide engine did not go well, and a lot of steam went out of the project, in quite a literal sense. When the Americans succeeded in designing a nuclear reactor suitable for fitting in submarines, a new era began and the HTP project was abandoned. Neither Explorer nor her sister Excalibur had much contribution to make in these circumstances, and they were scrapped in 1969/70.
