Plan Z:
British Light Cruisers
by Mike Bennighof, Ph.D.
November 2018

Britain’s Royal Navy entered the Second World War with a huge list of world-wide commitments. Warships needed to show the flag in foreign ports, guard British commerce (and that of other nations, thereby enhancing British prestige), and assure protectorates that they were indeed protected. Though chiefly symbolic, these missions did require ships that could back up the bluster. Battleships couldn’t be parceled out around the globe, while destroyers lacked both the range and physical impressiveness. The Royal Navy needed cruisers, and believed 70 such ships would be needed to fulfill its missions

In the mid-1930’s Britain laid down a huge class of light cruisers to replace aging veterans of the Great War. The Crown Colony class officially displaced 8,000 tons, to meet the new limits of the Second London Treaty (in reality they came in slightly overweight). Eleven ships were laid down in 1938 and 1939, entering service between 1940 and 1943. Eight of the ships carried 12 six-inch guns, while three had just nine. They saw hard service during the war in all theaters; one, Trinidad, becoming unfortunately famous for torpedoing herself while escorting a convoy to Murmansk.

Increasing need for light anti-aircraft weaponry, new electronics (fire-direction and radar) and the crews to handle both made the cruisers seriously top-heavy, leading to the re-design of three ships while fitting out to remove “X” turret (the super-firing position aft). The turret would be removed from four other ships during the course of the war; two were sunk before the modification could be carried out and only two finished the conflict carrying all 12 six-inch guns.

The follow-on Swiftsure class of eight ships in two subclasses would have been laid down in 1941, but wartime needs delayed the start of construction of several. Of the first group (of two ships), one cruiser completed in 1944 (and was then transferred to the Royal Canadian Navy) and the second a year later. Only one out of six of the second group would be completed to the original design, commissioning only after the war had ended.

An enlarged Crown Colony design, Swiftsure carried nine six-inch guns from the start and greater allotments of fuel and anti-aircraft weaponry as well as the latest electronic suite. As an additional weight-saving measure, she had no aircraft (these having been removed from the Crown Colony class during the war as well). Like the previous class, she had six torpedo tubes, minimal armor protection and a top speed of 31.5 knots.

Design changes came even as construction slowly continued, with the main battery of 6-inch Mark XXIII guns replaced, on paper at least, by the far more capable dual-purpose Mark XXIV which featured automatic tracking and radar fire control against both surface and aerial targets. The new-model turrets would not fit the Swiftsure hull, requiring a re-design and some re-construction were they to be used on the ships then under construction. Rather than invoke further delays and cost overruns, the third ship (Superb) was completed with the older weapons instead. The new turrets, guns and fire control equipment were all completed, but immediately put into storage at war’s end and never used.

Of the five uncompleted ships, two were eventually broken up on the slipways with the other three held there for over 15 years before they were finally launched as re-designed Tiger-class cruisers; two of these would be converted into helicopter-carrying cruisers in the 1960’s. The Royal Navy considered many alternatives for Swiftsure and her sisters, including razing Swiftsure to her main deck and rebuilding her as through-deck helicopter carrier. But in each case, the small size of the hull made modernization difficult at best, and terribly cost-inefficient. A great deal of money would be poured into attempts to make these cruisers efficient fighting ships for the Cold War Royal Navy, but like a number of other British ventures during this period these ended up merely wasting the Admiralty’s limited funds.

Aware that the cramped hull would make Swiftsure obsolete well before her time, once the outbreak of war lifted treaty limitations the Royal Navy pushed for a new class of light cruiser. The Neptune class (sometimes called the Mars class; as they were never authorized their names were only proposed, not official) would be almost twice the size of the Swiftsure and Crown Colony classes. At 15,000 tons they would carry a dozen of the new dual-purpose Mark XXIV six-in guns (or possibly the even newer Mark XXV which featured even greater elevation), with a full suite of radar fire control and automatic tracking. With their greater range, heavier shells and radar control, it was hoped that these guns would be effective against the high-speed jets and high-flying bombers expected to enter enemy arsenals.

Additionally, the cruisers would carry a dozen Mark V 4.5-inch dual-purpose guns in six twin mounts, already proven as a very effective anti-aircraft weapon plus 20 40mm Bofors guns in new radar-controlled mounts plus a large array of 20mm guns. That would make them very effective anti-aircraft escorts for the new aircraft carriers also planned or under construction. And for surface battle, in addition to the rapid-firing main battery they would have the astounding total of sixteen torpedo tubes.

Armor protection would be a step up from the Crown Colony and Swiftsure classes, particularly the armored deck. And they would have had vastly improved internal subdivision. Their speed would also be improved, to just over 32 knots.

Once again, the architects working for Britain’s Director of Naval Construction had produced a far better design than the hastily- and poorly-drafted fantasy ships of the German Plan Z. The Neptune class cruisers would have been much better fighting ships than their predecessors, and well-suited to carry on into the looming Cold War era. But Britain was no longer great, at least in financial terms, and the projected class never received funding. The Admiralty hoped to build five of the ships, plus transfer the contract for the Swiftsure-class Bellerophon to this design for a sixth unit.

Our Second World War at Sea: Plan Z expansion set includes all six projected Neptune-class cruisers. They are very useful vessels, a good mix of speed, firepower, anti-aircraft capability and (at least as cruisers go) protection.

The set also includes six of the Swiftsure class, without the Canadian ship (Plan Z concentrates on Royal Navy ships only; we’ll get to the Dominions later) or Bellerophon (which appears as a Neptune-class cruiser). They’re not bad fighting ships, at least by the standards of 1939, and they’re better warships than the German M class light cruisers, but are in no way comparable to the mighty Neptune.

Click here to order Second World War at Sea: Plan Z right now.

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Mike Bennighof is president of Avalanche Press and holds a doctorate in history from Emory University. A Fulbright Scholar and award-winning journalist, he has published over 100 books, games and articles on historical subjects. He lives in Birmingham, Alabama with his wife, three children and his dog, Leopold.