During the inter-war years Great Britain never really defined her naval policy in the event of another world war. For years such a conflict was deemed unthinkable, and so planning tended to be based around Britain’s imperial needs, the requirements of her peacetime fleet, and the naval strategy and tactics that had evolved during War War I. During the 1930s the growing threat posed by Germany, Italy and Japan forced the Admiralty to define the cruiser’s role in any future conflict. In theory they were the most flexible group of warships in the navy. Cruisers were fast, well-armed and could usually perform a range of naval roles. The heavy cruisers and Britain’s older light cruisers were earmarked to fulfil the long-established role of protecting the sea lanes and hunting down enemy raiders. However, they could also be used to support the main battle fleet if required. While the light cruisers built during the 1930s could also fulfil this role of commerce protection, there was no clear pre-war definition of what the navy expected of them.
Traditionally cruisers had been used to scout for the enemy, but that job was now better left to aircraft. Light cruisers were also too valuable and unwieldy to use to hunt enemy U-Boats – that task was best left to destroyers and smaller escort vessels. As war approached the Admiralty felt that the greatest assets of its new light cruisers were their firepower, speed and manoeuvrability. This made them well suited to providing anti-aircraft protection for convoys or task forces and for bombarding enemy coasts. They could also be used more aggressively to attack enemy surface forces or to raid their sea lanes. In the end this was exactly how Britain’s light cruiser force was used. It escorted the Arctic and Malta convoys in the face of enemy air attacks, it bombarded enemy positions in support of landings in north-west Europe and the Mediterranean, and it fought its Italian and German counterparts in swirling surface actions, where the cruisers’ combination of firepower and good fire control systems proved highly effective.
The E class cruiser HMS Emerald viewed in profile in Scapa Flow during the spring of 1943. At this time she carried a mixture of outdated single-mounted 6-inch guns, augmented by light AA guns, and a comprehensive radar suite.
For the most part Britain’s wartime light cruisers were equipped with two types of ordnance; the 6-inch gun or the 5.25-inch gun. The move away from 8-inch guns came about as a result of the London Naval Treaty, and it also led to the abandonment of smaller calibre cruiser ordnance in favour of the 6-inch Mark XXIII Breech-Loader (BL) gun. In all, around 469 of these guns were produced, making them the most commonly used medium calibre breech-loading gun in the fleet. The first 6-inch breech-loaders had been introduced into the navy in 1879, and during World War I more modern versions of the weapon were used to provide secondary batteries in armoured cruisers and battleships, and as a main battery weapon in some smaller cruisers. The Mark XXIII was essentially a slightly modified version of these earlier weapons. It was therefore somewhat old-fashioned, as it was loaded manually and relied on a secondary bagged cordite charge, but it was reliable, accurate and effective.
The real difference between the 6-inch Mark XXIII and earlier 6-inch guns was its mounting. It was compact and well suited to being incorporated into a twin or triple turret. Designs for these turrets were approved by the DNO in 1930 and 1932 respectively, and these were duly incorporated into the design for the British Leander and Arethusa classes (using twin Mark XXI mountings), the Southampton class (with triple Mark XXII mounts), and finally the Edinburgh, Fiji and Swiftsure classes, which used triple Mark XXIII mountings.
The original intention was that these guns would be used to engage aircraft as well as surface targets, so that the guns would create a flak barrage to prevent enemy aircraft from approaching the fleet. The turrets were designed to permit very high gun elevation, but it was soon discovered that a combination of relatively slow rate of fire and turret rotation and training meant that the guns were unsuited for this role. However, as conventional guns they proved very effective, with a range of just over 24,000 yards (12 nautical miles). While these guns fired accurately, when the triple turret was first introduced into the Southampton class it was found that the fall of shot was too scattered. On investigation it was discovered that the shell from the central barrel was deflected slightly by the blast of the two outer guns. This problem was soon solved by setting the central barrel back slightly inside the turret and using an electrical circuit to delay firing by a second.
The big advantage of these guns in action came about as a result of their relatively old design. While guns with automatic or semi-automatic loading systems could only fire at their prescribed rate of fire, it was discovered that these manual-loading 6-inch guns could attain a much higher rate of fire for short periods, as the gun crews were able to outperform guns that relied on more automated forms of loading. British light cruiser crews could therefore increase their rate of fire considerably until the loading speed dropped again as the crews tired. This was often enough to give the British light cruisers an edge over their Italian opponents and their more modern semi-automatic guns and turrets. However, it was not possible at long range – over 10,000 yards (5 nautical miles) – as it took longer for the guns to elevate from their loading to their firing positions. At a range of 12,000 yards (6 nautical miles) these guns could penetrate 3 inches of belt armour, or 2 inches of deck armour at ranges over 20,000 yards (10 nautical miles). This made them more than a match for most Italian cruisers, heavy or light.
| 6-inch Breech-Loader Mk XXIII | |||
| Calibre | 6-inch | Rate of fire | Six rounds per minute (seven to ten rounds for brief period) |
| Date of design | 1930 | Weight of shell | 112lb |
| Date first in service | 1931 | Shell types | High explosive, armour piercing |
| Length of bore | 50 calibre (300-inch) | Weight of propellant charge | 30lb (‘supercharge’) |
| Length of barrel | 310 inches | Muzzle velocity | 2,758fps |
| Weight of gun | 6.9 tons | Maximum range | 25,480 yards |
| Mounting | Twin Mark XXI Triple Mark XXII or Triple Mark XXIII | Ammunition storage per gun | Varies, depending on cruiser, but 250–300 rounds was typical |
| Maximum elevation | 60 degrees Later reduced to (45°) | Estimated barrel life before replacement | 1,100 rounds |
| Range and velocity (given for armour-piercing shells) | ||||
| Gun elevation | Range | Strike velocity (feet per second) | Angle of descent | Flight time |
| 2.25° | 5,000 yards | 1,939fps | 3° | 7 seconds |
| 6.25° | 10,000 yards | 1,371fps | 10° | 16 seconds |
| 13° | 15,000 yards | 1,098fps | 23.5° | 30 seconds |
| 39.5° | 20,000 yards | 1,087fps | 40° | 47 seconds |
| 41° | 25,000 yards | 1,159fps | 56.5° | 72 seconds |
| 41.5° | 29,000 yards | 1,240fps | 79° | 79 seconds |
In the Dido and Bellona class anti-aircraft cruisers, the main gun was the 5.25-inch Quick-Firing (QF) gun, Mark I, the largest quick-firer in British wartime service. Exceptions were the Dido class cruisers Scylla and Charybdis, which were fitted with 4.5-inch QF guns instead. This was a dual-purpose gun, designed primarily as an anti-aircraft weapon, but which could also be used to engage surface targets if required. In these cruisers the guns were mounted in compact twin Mark II mounts, much smaller than the 6-inch turrets carried on other cruisers. These turrets usually performed well, but there seemed to be a problem with ‘A’ turret in the Dido class as the flexing of the flimsy bow sometimes jammed the turret. This happened in April 1940, when the brand new Bonaventure was engaging the German heavy cruiser Admiral Hipper off the Norwegian coast. The problem was easily rectified by strengthening the bows of the Dido class.
A cutaway view of a southampton class cruiser as she would have appeared during the opening year of the war, from a contemporary publication entitled Britain’s Glorious Navy. While it shows the location of her haCs gunnery direction towers, this vessel lacks any of the radars or light aa guns that were fitted to warships of this class from 1940 onwards.
The greatest advantage royal Navy light cruisers enjoyed over their axis opponents was radar–search, air warning and fire control sets being fitted from 1940 onwards. this diagram shows how visual and radar-guided fire control information is processed and used to direct the fire of the cruiser’s main 6-inch battery.
The Norwegian campaign of April 1940 first demonstrated the true potential of these guns in surface actions. With a maximum range almost as good as that of the 6-inch gun and with the semi-automatic mounts providing a greater rate of fire, these ships were able to – and occasionally did – stand in the line of battle alongside 6-inch light cruisers during surface engagements with the Italian fleet. As the semi-armour-piercing (SAP) round could penetrate 3 inches of armour at 9,000 yards (4.5 nautical miles) this meant they had to get considerably closer than the 6-inch cruisers to inflict serious damage on enemy cruiser-sized vessels, but they could still more than hold their own in a close-range fight.
| 5.25-inch Breech-Loader Mk I | |||
| Calibre | 5.25-inch | Rate of fire | Seven rounds per minute |
| Date of design | 1935 | Weight of shell | 80lb |
| Date first in service | 1940 | Shell types | High explosive, semi-armour piercing, starshell. From 1945 anti-radar |
| Length of bore | 50 calibre (262.5-inch) | Weight of propellant charge | 18lb (‘supercharge’) |
| Length of barrel | 275.5 inches | Muzzle velocity | 2,672fps |
| Weight of gun | 4.3 tons | Maximum range | 25,070 yards |
| Mounting | Twin Mark I Twin Mark II | Ammunition storage per gun | 340 rounds |
| Maximum elevation | 70 degrees | Estimated barrel life before replacement | 750 rounds |
In most wartime light cruisers from the Leander class onwards, the primary anti-aircraft weapon was the 4-inch Mark XVI QF gun, usually mounted in twin Mark XIX turrets. These turrets were HA/LA mounts, meaning they could fire at high and low angles against dive bombers and torpedo bombers respectively. Using the HACS director, these guns would put up a curtain of flak to deter enemy aircraft, and using Type 285 (fitted to most light cruisers after 1942–43), these could react quickly to counter incoming aircraft. They were even capable of shooting down attacking aircraft in their own right. Carlisle, carrying four of these mounts, shot down a total of 11 aircraft in the Mediterranean before she was almost destroyed off Greece in late 1943. In April 1940 she also used her 4-inch guns to sink a German transport ship off Norway, thereby demonstrating that in extremis these guns could be used against surface targets.
Just as effective were the lighter anti-aircraft weapons that were added to these light cruisers in increasing numbers as the war went on. Early war mounts such as single 2-pdrs, quad ½-inch machine guns and the cumbersome eight-barrelled 2-pdr ‘pom-pom’ were eventually replaced by more versatile quadruple ‘pom-poms’, single- and twin-mounted 20mm Oerlikons, then power-mounted versions. Finally, in some cases 40mm Bofors guns were added, either in single or quadruple mounts. Like the 4-inch guns, what made these light AA weapons more effective was the addition of radar fire control. Air search radars prepared the AA gunners for what was coming, and then sets like Type 282 and 285 helped feed information to the AA batteries during an air attack.
Less useful were the suite of torpedoes carried on board most light cruisers, and the aircraft with their attendant facilities. Both proved a liability in action as a hit on their position could cause an explosion or fires, and they were deployed with such infrequency that the ships were probably better off without them. As more fleet destroyers and aircraft carriers entered service the need for these weapons diminished, and so most were removed from the cruisers as the war progressed.
HMS Edinburgh as she appeared shortly before her loss in April 1942. She carried a new suite of surface search and fire control radars, fitted during a refit in Tyneside earlier that year. Edinburgh carried this striking camouflage pattern from October 1940.
What really gave British light cruisers an edge over their wartime opponents was the highly effective combination of sensors and fire control they carried. While few cruisers had radar fitted before 1941, the number of sets proliferated, at least on ships that had survived the first gruelling naval campaigns of the war. In 1938, Sheffield was fitted with a Type 79 air warning radar, capable – if the conditions were right – of detecting enemy aircraft up to 60 miles away. If the enemy aircraft were Ju 87 Stukas, this gave the gunners 20 minutes advance warning of an air attack. The set then evolved into the versatile Type 279 radar, which combined its air warning function with a surface search capability.
There was a difference between ‘broad beam’ radar sets which were used for air and surface search – their effect likened to a floodlight – and ‘narrow beam’ sets, which were used to gather precise location and targeting information, like a torch or flashlight directed at the target. The Type 286 surface search radar and the Type 279 or Type 281 air warning sets fitted to many light cruisers during 1941 were both ‘broad beam’ sets, while the Type 284 main gun fire control radar was a ‘narrow beam’ radar.
Even before the advent of radar, British cruisers had well-tested visual fire control systems for use against surface or air targets. For instance, the HACS helped direct the cruiser’s main anti-aircraft guns (usually the 4-inch batteries) by calculating the height and bearing of incoming aircraft, and then passing this information on to the gun positions. This hydraulically driven system relied on visual targeting and worked well if the attacking aircraft maintained a constant course, altitude and speed. Unfortunately not all enemy aircraft were so obliging; for instance the system was particularly ineffective as a means of countering attacks by enemy dive bombers such as Stukas.
What gave the HACS a new lease of life was its integration with the Type 279 air warning radar, which allowed the operators to track every change of enemy course, speed and bearing. By late 1941 the light cruisers equipped with this radar had proved highly effective at countering enemy air attacks. Fiji was fitted with Type 279 radar, and in action off Crete in May 1941 she held off repeated enemy air attacks. She was finally bombed and sunk when her ammunition ran out.
By late 1941 the even better Type 285 radar began to be fitted to cruisers. Improvements continued until the end of hostilities. Secondary AA guns (or main batteries in the case of anti-aircraft cruisers) could also use the Type 283 radar and its attendant Auto Barrage Unit (ABU) to throw up heavy flak barrages in the path of incoming aircraft. This wall of flak proved just as deadly to aircraft as directly aimed AA fire. By 1943 radars such as the Type 282 were used to direct the fire of light AA guns, guided by directional antennas and automated precision ranging. The aim of all this electronic fire control was simple – it made sure the guns were pointing towards the oncoming threat and were able to counter any manoeuvres the aircraft made while they were within range of the cruiser’s guns.
Main gun batteries were provided with at least one Director Control Tower (DCT), but most of the larger light cruisers had two. They were trainable, and their crew tracked the enemy using stereoscopic rangefinders and passed information on the enemy’s range, course, bearing and speed to the transmitting station (TS). There this information was rapidly analysed to produce a firing solution for the guns. The crew of the DCT also observed the fall of shot, and so corrected the aim of the guns until their shells were hitting the target.
This form of visual fire control was used by the light cruisers Ajax and Achilles during the battle of the River Plate. On the morning of 13 December 1939 they engaged the German pocket battleship Graf Spee, supported by the heavy cruiser Exeter. The way the battle was fought was similar to the naval engagements of World War I, as gun direction teams used magnified rangefinders to track the enemy and to direct the fire of the guns. During the battle Ajax and Achilles closed the range as quickly as they could to maximize the effectiveness of their 6-inch guns. While the Graf Spee concentrated her fire on Exeter, they forced the German battleship to split her fire and so probably saved Exeter from destruction. The light cruisers closed the range to less than 10,000 yards (5 nautical miles) and fired all they had at Graf Spee, including torpedo spreads. The German pocket battleship withdrew from the fight, and the British light cruisers shadowed her until she entered neutral waters off Montevideo.
Ajax was hit several times during the battle and her after turrets were hit and damaged. Her DCT was also damaged, but its surviving crew continued to feed targeting information to the guns using secondary rangefinders. Achilles fought much of the battle with her turrets under local control – individual spotters in each turret corrected their own shot. At such short ranges this less sophisticated system was probably just as effective, and more responsive. Ajax also launched her Fairey Seafox seaplane, which provided spotting information to the gunnery direction team during the battle by observing fall of shot. This was an old-fashioned battle, fought in a way that had changed little since the battle of Jutland.
This system of visual fire control was similar to those employed by Britain’s enemies. What gave the Royal Navy an edge over its opponents was the integration of this already sophisticated system with radar. This could be used to augment visual gunnery control, and it also allowed the cruiser to fire ‘blind’ using radar fire control alone. The Germans, Italians and Japanese never reached anything like the same sophistication in radar fire control, and this advantage provided the British with a major advantage over their opponents. In 1941 the Type 284 main battery fire control began to be introduced into light cruisers, and the following year an improved version was developed that was more reliable, easier to operate and considerably more accurate. It could even detect shell splashes, and so could be used to ‘walk’ salvos onto the target.
Of course the real test of these fire control systems was whether they worked in action. During the battle of North Cape, fought in December 1943, Vice-Admiral Burnett’s flagship Belfast and the cruisers Sheffield and Norfolk detected the German battlecruiser Scharnhorst as it tried to intercept an Allied convoy off the northern coast of Norway. At the time Belfast carried Type 273 target identification radar and Type 284 main battery fire control radar, as well as other air warning and secondary fire control sets. Sheffield and Norfolk carried a similar radar suite. At 9am on 26 December the cruisers detected Scharnhorst by radar and engaged her at a range of 6 nautical miles. The unsuspecting German battlecruiser still had her guns trained fore and aft. She was hit twice, and her own primitive radar set was knocked out. She disengaged and the British cruisers shadowed her by radar, reporting her position to Admiral Fraser on board the battleship Duke of York. By early evening Fraser was in a position to engage Scharnhorst, supported by the cruiser Jamaica and Burnett’s Belfast. The battle that followed was fought in a blizzard, but the British battleship and light cruisers used their fire control radars to track and engage the enemy. The Scharnhorst was eventually sunk – a victory that owed as much to the new technology of radar fire control as it did to British naval firepower. This engagement shows just how far British naval technology had come since 1939.