The Roberts class

When war broke out, a newly refurbished Erebus was in Portsmouth, earmarked for the defence of Cape Town in South Africa, while Terror was undergoing a refit in Singapore. Both monitors had been brought back into active service in 1933, to augment the coastal defences of naval bases overseas. Marshal Ney and a few of the smaller monitors still existed, but most were unarmed, and all were incapable of resuming their old roles as monitors. So, the new First Lord of the Admiralty Winston Churchill pushed the rest of the Board of Admiralty to modernize the two Erebus-class monitors, and gather them in home waters, where they could be used in a naval gunfire support role if required. At the same time, Sir Stanley W. Goodall, who had held the post of DNC since 1936, was instructed to brush off his department’s old monitor plans, update them, and then submit the modified versions for a new pair of 15in.-gun monitors.

Goodall though, despite his poor health, was something of a perfectionist, and while clearly based on earlier big-gun monitors, his plans were a major development of them, bringing the design into a more modern age, and eminently suitable for naval operations in this new conflict. The twin 15in. gun turrets were repurposed. The one for HMS Roberts, namesake of the new class, would be provided by the one taken from the monitor turned gunnery drill ship Marshal Ney, while the one for the sister ship HMS Abercrombie was a spare turret, earmarked for the battlecruiser Furious in late World War I, if the single 18in. gun turrets designed for the ship proved technical failures. They would then be replaced by 15in. gun ones. In the end, the conversion of Furious into an aircraft carrier rendered both 15in. and 18in. turrets surplus to requirements. Apart from the turrets, the two Roberts-class monitors were thoroughly modern warships.

Their design, though, while noticeably improved, was broadly similar to its predecessors. Most of this was carried out by M. C. Dunstan, the Admiralty’s Assistant Director of Naval Construction, who, given the need for speed in design and construction, was happy to take an older design and modernize it. The Roberts-class monitors that Dunstan designed would be just over 30ft shorter, with a slightly greater draught, but otherwise would be broadly similar to their Erebus-class predecessors. The main difference, apart from their generally more modern appearance, was their engines, which could make 12 knots. This was still slow, especially when the monitors were on long ocean passages, but the speed was considered adequate for their main operational purpose – naval gunfire support. A suggestion to use diesel engines was considered, but the idea was abandoned as these would take longer to build and install.

Their already beamy hulls were widened further by the addition of anti-torpedo bulges, like those fitted in the earlier class, but modernized, following the style adopted in the new King George V-class battleships. These bulges were made up of three compartments: a water-filled one running the length of the bulge, sandwiched between two air spaces, an outer one and an inner one, both of which were divided into small compartments. This system was meant to be proof against most modern torpedoes. A 4–5in.-thick armoured belt was provided for the hull, sloped at a 35°angle, to protect the hull from long-range fire. This was considered proof against fire from 6in. coastal guns. The turret face was covered by 13in. steel plate, while the turret sides and exposed barbette had 8in. of protective armour. With air attack in mind, the monitors’ main deck was protected by 3in. of steel plate, proof against a direct hit from a 500lb (227kg) bomb. The conning tower was protected too, with up to 3in. of armour.

The appearance of the Roberts-class monitors differed from their predecessors. The main twin 15in. gun turret still dominated the ship, raised up on its exposed but armoured barbette. Behind it was a similar but more modern bridge superstructure, including the conning tower, charthouse, signal offices and compass platform, but integrated with it, rather than freestanding behind it, was a tripod foremast, supporting the 15in. gun director and spotting top. There was a smaller mainmast as well, further aft, emerging from the after superstructure, which housed a Type 282 radar room, which controlled the AA battery, as well as an HACS High-Angle Control System – the AA rangefinder/director, and a twin 4in.-gun mount. Further aft, above the shelter deck, was an eight-barrelled 2-pdr (40mm) ‘pom-pom’ AA gun, which had a good arc of fire over the stern half of the ship.

Roberts was laid down in the John Brown shipyard in Clydebank in late April 1940, just before the debacle of Dunkirk. She was launched the following February, and after fitting out, was commissioned into the Royal Navy in late October 1941. The monitor’s turret was taken from the older monitor Marshal Soult, which was no longer considered seaworthy. Abercrombie was laid down a year later, in late April 1941, due to a lack of shipyards free to do the work. She was eventually built in the Vickers-Armstrong Naval Shipyards in Newcastle and was launched into the Tyne 11 months later, in March 1942. During the monitor’s fitting out, Abercrombie’s main 15in. turret was provided, as described previously, from a spare one, once earmarked for the light battlecruiser Furious. The monitor was finally commissioned in early May 1943.

You can read more in Royal Navy Monitors of World War II.