Diadem - class cruiser The " Diadem " class cruiser was a class of " First - Class " protected cruiser built for the Royal Navy during the 1890s that served in the First World War . The class consisted of eight ships , built at a cost of around £600 , 000 each . They were considered " good sea boats " but criticised for their lack of a heavy calibre main armament , bulky unprotected sides , average speed and lack of manoeuvrability despite being considered large ships when completed . They were the last British first class protected cruisers ; the armoured cruiser taking the large cruiser role in future . " Design . The " Diadems " were designed by Sir William White , and are typical of British design practice of the period , with high freeboard ( by the standards of the time ) and the use of ' double - decker ' casemates , with the hull forward and aft cut away to allow fore and aft fire from the casemate guns . Casemates provided good protection for the guns and allowed a large number of guns to bear on the broadside ; however , the lower ( main deck ) guns were almost unusable in heavy seas . According to a contemporary ( 1900 ) edition of Jane ' s Fighting Ships : History . The " Diadem " class was intended , like the preceding " Powerful " class , for trade protection , and were intended to be " capable of dealing with any cruiser existing or building " . The " Powerfuls " had proved costly and demanding in manpower , and the new class had to represent a more economical solution , that could be built and operated in greater numbers . To achieve this , the specification was reduced relative to the " Powerfuls " : power and speed were reduced from 25 , 000 ihp ( 22 knots ) to 16 , 500 ihp ( about 20 knots ) , the thickness of the protective deck reduced from 6 to , and the armament simplified by replacing the single guns fore and aft with pairs of guns , mounted side by side . These changes saved about £100 , 000 per ship ( approximately 15 % ) relative to the " Powerful " design . With eight ships , each of 11 , 000 tons and costing £600 , 000 , the " Diadems " were an important class . However , they proved controversial . The naval journalist Fred Jane characterised them as " much - discussed " and complained that " all the weak points of the " Powerfuls " were exaggerated in them " . In particular , contemporary critics raised objections to their indifferent speed , poor manoeuvrability , and lack of heavy guns , and the fact that , while most of the armament was well protected in casemates , the fore and aft pairs of guns , which commanded the greatest fields of fire , were protected only by gunshields . Although the powerplant used Belleville boiler s , which were of the then - new water - tube type , most of the ships enjoyed the reputation of good steamers ; the exception was " Niobe " , whose engines gave persistent trouble . The first four ships were troubled by vibration ; to remedy this , the engine rooms of the last four was rearranged ; the new configuration also provided a increase in power . All eight ships exceeded their design power on trials ( for details , see below ) ; the first four averaged in service , the later four . In general the " Diadems " served most of their careers in home waters , although there were some deployments to China Station , the Mediterranean and the Caribbean . " Niobe " was sold to Canada in 1910 . After 1906 , they were only occasionally in commission , and by 1914 the class had for the most part been relegated to training ship and depot ship duties . However , with the outbreak of the First World War , several of them were reactivated , initially for patrol duties with the 9th Cruiser Squadron in the Eastern Atlantic . In 1917 " Amphitrite " and " Ariadne " were converted into minelayer s , for service with the Dover Patrol . " Ariadne " was the only war loss , being torpedoed by the German submarine UC - 65 on 26 July 1917 . By the end of the war the survivors had again been withdrawn from active service , and all of them had been sold for scrap by 1932 , with the exception of " Andromeda " , which served as a boys ’ training ship until 1956 . Building Programme . Standard British practice at that time was for building costs to exclude armament and stores . Trials . The " Diadem " ( Dec 1898 ) did a mean of in a 69 hour run from Gibraltar to the Nore with 14 , 268 horsepower ( 10 . 64 MW ) . For 60 hours with 24 boilers with 12 , 791 ihp ( 9 . 538 MW ) , she made on trial . " Andromeda " did a sea trip at = .