BL 18 Inch Mk I Naval Gun - Design and Development

Design and Development

The 18-inch gun had its genesis in the insistence of the First Lord of the Admiralty, Admiral Fisher, for the biggest possible gun mounted on the fastest possible ship. He conceived of what he called "large light cruisers" carrying four 15-inch (380 mm) guns, which became the Courageous-class, but he wanted their half-sister Furious to carry an even bigger gun. The Elswick Ordnance Company was the only company capable of manufacturing such a large gun and began design work in 1915. It was designated as the "15-inch B" to conceal its real size and was derived from the design of the 15-inch Mk I already in service.

As mentioned above, these were wire wound guns whose construction generally resembled that of the 15"/42 (38.1 cm) Mark I but with a relatively small breech ring. Construction consisted of inner A tube, A tube, wire-winding, B tube, jacket, shrunk on collar and breech ring. Over 200 miles (325 km) of 0.25 × 0.06 in (0.635 × 1.52 cm) of high-tensile steel wire was used. The Welin breech block use on these guns was significantly different in that the Vickers' "pure couple" mechanism of the 15" (38.1 cm) was replaced with the Elswick short arm mechanism, for reasons of reducing "slam" as the breech closed. In this design, the breech screw withdrew through the carrier, which complicated the locking action. However, this mechanism was fast-acting, with about three seconds being needed to open or close the breech.

The gun and its breech mechanism weighed a total of 149 long tons (151 t), almost half again as much as the 15-inch gun's 100 long tons (102 t). It was mounted in a single-gun turret, also designated as the 15-inch B, derived from the twin-gun 15-inch Mark I/N turret. The barbettes of Furious were designed to accommodate either turret, in case problems arose with the 18-inch gun's development. The gun could depress to −3° and elevate to a maximum of 30°. Ammunition development for the gun was naturally focused on anti-ship shells for the Furious, and it fired a 3,320-pound (1,510 kg), 4crh armour-piercing, capped (APC) shell, at a muzzle velocity of 2,270 ft/s (690 m/s) to a distance of 28,900 yards (26,400 m). It could fire one round per minute. The turret's revolving mass was 826 long tons (839 t), only a slight 2% more than the 810 long tons (823 t) of its predecessor.

The guns proved to be too powerful for Furious' light hull, and they became available for other uses during 1917, after trials showed the ship could not handle the stress of firing. Admiral Sir Reginald Bacon, commander of the Dover Patrol, conceived a plan to mount two guns inside the shell of the Palace Hotel in Westende from where they could bombard the naval facilities at Zeebrugge and Bruges, provided that the hotel was captured during the upcoming Battle of Passchendaele. He planned to transport the guns across the English Channel lashed to the torpedo bulges of monitors. He also thought that they could be used on the decks of monitors and as such a dual purpose carriage was designed for the guns, that could be used both afloat and ashore. Only a limited amount of traverse was required for either role, but elevation had to be increased to 45° to maximize range. The concept was approved 23 September 1917, and Elswick was ordered to design the new 'B CD' mounts for delivery in five months.

The original concept for land use involved a special elevating slide that could traverse 6° to either side. Ammunition handling, elevation and ramming were to be done via hydraulic pump, but the breech was hand-worked. The gun was to be installed in a turf-covered concrete dome with a gunport for the barrel. As much as possible of the gun and its mount was designed to be assembled out of range of German artillery and then moved on a special broad-gauge railway to the site on specially-designed wheels. The transportable section weighed 210 long tons (213 t).

After the British Army failed to capture Westende, the mounting was optimised for use on a monitor. It was very simple, consisting of two large girders connected together at each end with the gun and its carriage between them. The mount could only traverse 10° inside its fixed, ½-inch (12.7 mm) gun shield and was aimed over the starboard side of the monitor. It was loaded at a fixed angle of 10°, but it could only fire between 22° and 45° to equalize the stresses on the carriage and the ship. It was provided with hydraulically powered cranes, loading tray, rammer and breech mechanism to minimize the crew's workload, but the ammunition parties had to use muscle power. The shells were stowed below deck and had to be moved by overhead rail to the hatch in the deck behind the gun to be lifted up and loaded. The cordite propellant charges were kept in eighteen steam-heated storage tanks mounted on the forecastle deck abaft the funnel and moved to the gun on a bogie mounted on rails, two one-sixth charges at a time, which reduced the rate of fire to about one round about every 3–4 minutes. The monitors had to be extensively modified to handle the gun. Numerous additional structural supports had to be added underneath the gun to support its weight of 384 long tons (390 t); the sides had to be plated in to accommodate the additional crewmen and the interior rearranged for the 18–inch shells and the loading arrangements.