The Jewel Class Coast Defence Cruisers were ordered as a contrast to the huge cruisers and battleships that were then under construction. Those same huge ships were not really suitable for chasing round the coasts of Atlantis chasing smugglers. Atlantis had such a large amount of gems available to be mined that it was natural that some 'smart' people would try to smuggle out contraband gems and avoid paying the Government taxes. Eventually it was the advent of the aircraft and radar that put paid to this lucrative sideline.
Six ships were ordered. Diamond, Sapphire, Emerald, Ruby, Opal, and Topaz. The first two completed in 1916 and the other four completed in 1917. Two were retained in home waters (alternating with those posted overseas) of which one, the Opal ran down and intercepted a German raider that was on its way in to bombard one of the Atlantean port areas. The ensuing battle lasted several hours with the Grief trying to get away at 18-19 knots while the oil fired Opal made 20 knots and ran down the Grief to a point where it started hitting the German ship. Once the hits were happening the end came quickly into sight. A puff of steam, a couple of puffs of smoke and the speed of the Grief dropped away to a crawl. The Opal signaled for the Grief to surrender, but the Grief kept firing its last two 4.1" guns, so the Opal stayed out of range and a final couple of 9.5" broadsides made further hits on the Grief which slowly rolled over and sank. One of the class, Ruby, was lost at the Dardanelles, to mines, the rest made it through WW1.
The five remaining ships undertook various duties during the inter-war period, but their constant duty still remained coast defence and chasing smugglers. At twenty years of age the ships were surveyed for major upgrade work. The Navy had never been happy with the mixture of turret and casemate 9.5" guns. The casemates could only elevate to 18 degrees while the turrets elevation went up to 28 degrees. This made a large difference in the range of the guns. The advent of aircraft also made an impact on the future use of these ships on overseas postings in the war that was showing on the political horizons. It was time to rebuild and upgrade everything that could be useful.
Every eight months from the start of 1936, one of the five ships would be taken in hand for an 18 month rebuild. The biggest part of which was removing all the armament except the two main turrets and replacing it with a modern AA based armament. Nothing was done about the armour which with a 5" belt and 2" deck armour set, they were as well armoured as most modern cruisers. The engines were also not touched as they had never been run at maximum speed for any length of time and were still in reasonable condition (when compared to the destroyers of the same period).
War service for the five ships will be varied and still to come. It might take me a little while to dream up different scenarios for these ships and where they could be used.