Arethusa - class cruiser ( 1934 ) The " Arethusa " class was a class of four light cruiser s built for the Royal Navy between 1933 and 1937 and that served in World War II . It had been intended to construct six ships , but the last pair , " Polyphemus " and " Minotaur " were ordered in 1934 as the 9 , 100 ton Town class " Southampton " and " Newcastle " Design . The " Arethusa " s were a smaller version of the " Amphion " group of the earlier " Leander " class , having the unit machinery layout and two funnels of the former . The design was judged to be the minimum required for a " trade route cruiser " to counter the threat of the auxiliary cruiser over which , even with their reduced armament , they would enjoy a comfortable superiority . They were also to be capable of acting as a fleet cruiser ( which was fortunate because , in the end , they were used almost exclusively with the fleet ) . Therefore , no reduction in speed ( i . e . machinery ) could be accepted and savings had to be found in armament , size and protection ; the " Arethusa " s suppressed ' X ' 6 - inch gun turret and were shorter and displaced 1 , 250 tons less than the " Leander " s . The protection scheme was the same as the " Leanders " but was generally thinner to save weight . This allowed six " Arethusa " s to be built for every five " Leander " s within the constraints of tonnage allowed under treaties then in force . Welded construction was widely used for the first time to save weight , over 250 tons being cut off the original specification . They were armed with six BL 6 inch Mark XXIII in three twin mountings Mark XXI in ' A ' , ' B ' and ' Y ' positions . Triple Torpedo tubes were carried abreast the after funnel , the reduction in beam had reduced training space resulting in the omission of one tube " vis - à - vis " the " Leanders " . The secondary armament was four QF 4 inch Mark V on single mountings HA Mark III , controlled by a HACS director on the bridge . The 4 - inch magazine was retained in the position of the " Leander " class well forward , but the guns themselves were moved well aft . As a result , the 4 - inch shell and charge had to be transported along the ship to reach the guns . In " Penelope " and " Aurora " eight QF 4 inch Mark XVI on four twin mountings HA / LA Mark XIX replaced the single mounts , and a second HACS director was added aft . A shelter was added for the gun crews between each pair of guns as it was recognised that in wartime the crews would spend a lot of time closed up at action stations and would rapidly fatigue in the open gun mountings . " Galatea " received similar alteration before the outbreak of war . The light armament consisted of an eight 0 . 5 inch Vickers machine guns in two quaduple mountings . A rotating catapult for a float plane and a derrick were fitted between the funnels . It had been intended to carry a second aircraft aft , but in the end this never happened . " Aurora " completed without aircraft facilities , and had a deckhouse for accommodation in lieu for service as Commodore . Modifications . " Aurora " received a Unrotated Projectile ( UP ) mounting and eight QF 2 pounder Mark VIII in two quadruple mountings Mark VII in the summer of 1940 . Radar Type 284 was added to the main armament director for taking ranges and bearings and Type 280 air warning at the mastheads was added in April 1941 . In August of the same year she received six single 20 mm Oerlikons and two quadruple 0 . 5 inch machine guns . In 1943 she received Radar Type 282 on the 2 pounder " pom - pom directors " . " Galatea " had extra plating added amidships after completion to reduce wetness and to protect the boats . She landed her catapult during a refit between October 1940 and January 1941 , when she received two quadruple 2 pounders and eight single 20 mm Oerlikons , as well as Radar Type 279 air warning added at the mastheads . " Arethusa " had received two quadruple 2 pounders and radar by April 1941 , and landed the catapult . Later the same year , two UP mountings and four single 20 mm Oerlikons were added . The former were removed in the spring of 1942 , as were the single 4 in mountings ( replaced by twins as per her sisters ) and a further four 20 mm Oerlikons added . Radar Type 286 air warning was landed and radars Type 273 centimetric target indication , Type 281 air warning , Type 282 on the 2 - pounder directors , Type 284 on the main armament director and Type 285 on the HACS directors were fitted . Three additional 20 mm Oerlikons were added by October 1942 . Between March and December 1943 , while under repair in the USA , the 2 pdr were supplanted by quadruple 40 mm Bofors mountings Mark II , three single Oerlikons by four twin power operated mounts Mark V and had the radar fit modernised . " Penelope " also lost her catapult and had two quadruple 2 pounders fitted between August 1940 and July 1941 . Four single Oerlikons were added at the end of 1941 , and four more in the summer of 1942 . By the end of the war , the surviving ships had around 700 tons of extra equipment added . Service . The " Arethusa " s proved to be very satisfactory in service and their hull was adapted for the " Dido " class of 1937 . All had a very active war especially in the Mediterranean ; the two that were lost were torpedoed while working close inshore . " Arethusa " had a narrow escape in November 1942 when she was hit by an air - dropped torpedo . She caught fire , had two of her three turrets out of action and was badly flooded . However she survived to be repaired at Charleston in the USA .