QF 6 inch /40 naval gun

The QF 6 inch 40 calibre naval gun was used by many United Kingdom-built warships around the end of the 19th century and start of the 20th century.

In UK service it was known as the QF 6 inch Mk I, II, III guns. As the Type 41 6-inch (152 mm)/40-caliber naval gun it was used for pre-dreadnought battleships and armoured cruisers of the early Imperial Japanese Navy built in UK and in European shipyards.

QF technology
These guns were developed to exploit the new "QF" technology, which involved loading the propellant charge in a brass case with primer in its base. The brass case also sealed the breech, allowing a lighter mechanism. This was presumed to allow a faster rate of fire than the older "Breech Loading" system, where the propellant was loaded in cloth bags and then a separate friction or percussion tube fitted into the breech for firing. The QF principle had proved successful with the much smaller QF 3 pounder Hotchkiss and Nordenfelt QF 3 and 6 pounders from 1885 onwards.

The Mk I was an Elswick gun of built up construction. Mk II was built by Woolwich Arsenal and in 1891 became the first Royal Navy gun using the Armstrong wire-wound construction. The breech mechanisms were developed from the existing 6 in BL mechanisms, but as it no longer had to provide obturation (sealing of the breech), the front was made coned rather than straight which allowed it to be swung round to the side before it was fully withdrawn, rather than having to be fully withdrawn before swinging to the side as with the BL gun.

Recoil system
The preceding generation of British 6-inch guns (BL Mks III, IV and VI) had old-style trunnions by which they were mounted on Vavasseur inclined slides to absorb recoil. QF Mk I and II dispensed with trunnions and instead on the lower side of the breech ring were lugs to which were attached modern recoil buffer and hydrospring recuperator (runout) cylinders to absorb recoil and return the barrel to loading position after firing. This allowed the gun to recoil directly backwards rather that backwards and upwards as previously, and is the recoil system which in essence is still in use.

Mk III was built by Elswick and was similar to Mk I except that it had trunnions which allowed it to be deployed on the remaining obsolescent but still in service Vavasseur recoil mountings. All 3 Marks had the same dimensions and performance.

Royal Navy service
As the QF 6 inch Mk I, Mk II and Mk III, the gun was used as secondary armament of pre-dreadnoughts of the 1890s and cruisers to 1905. On the armoured cruisers of the Diadem, Powerful and Edgar classes they made up most of the armament, though the latter class carried two 9.2 in guns as well. The pre-dreadnought battleships of the Royal Sovereign (including the turreted HMS Hood), Centurion, Majestic and Canopus classes carried up to 12 guns.



Second Boer War land service
During the Second Boer War one gun was brought ashore from HMS Terrible in Natal in February 1900 at the request of General Buller, presumably in response to the failure at Colenso. It was mounted on an improvised field carriage by Captain Percy Scott and transported by rail to Chieveley, just south of Colenso. There it was manned by Royal Navy gunners to provide useful fire support for the British Army during the relief of Ladysmith. It is reported on 17 February to have fired from "Gun Hill" (a small kopje 2 two miles (3 km) north of Chieveley ) and knocked out a Boer gun at 16500 yd, followed by a Boer searchlight, as Buller approached Ladysmith from the South East and pushed the Boers back towards the Tugela river. On 26 February Lieutenant Burne reports firing from the same position on a Boer gun at 15000 yd at 28° elevation and falling 200 yd short. The 7 ton weight (compared to the 2½ tons of the Boer 155 mm "Long Tom") meant that it was effectively immobile on the battlefield and could not be moved forward to shorten the range.

Two guns were also mounted on armoured trains, crewed by Royal Garrison Artillery men.

Coast defence gun
From 1894 a number of guns were adapted for coast defence use, with the original 3-motion breeches replaced by modern single-motion breeches to increase the rate of fire, which designated them as "B" guns.

Nineteen guns were still active in the defence of the UK as at April 1918 : Jersey (2), Guernsey (2), Alderney (2), Shoeburyness (2), Blyth (2), Clyde Garrison (1), Mersey (2), Berehaven Garrison (Bantry Bay, Ireland) (6).

World War I anti-aircraft gun
At least one gun is known to have been mounted by the Royal Navy on an improvised anti-aircraft mounting on a railway truck, defending the London docks during the First World War. 

Conversion to 8 inch (203 mm) howitzer
In World War I Britain urgently needed heavy artillery on the Western Front, and various obsolete 6-inch naval guns were converted to 8-inch howitzers. Sixty-three QF 6-inch Mk II guns were shortened, bored out to 8 inches (203 mm) and converted to BL type to produce the BL 8-inch howitzer Mk V. Four entered service in December 1915 and 59 followed in 1916. 

Japanese naval service
The Type 41 naval gun was designed by Armstrong Whitworth, Elswick, Newcastle upon Tyne, England as a slightly modified version of the Elswick Ordnance Company QF pattern 6 in guns used on contemporary Royal Navy battleships. It was the standard secondary armament on early Japan battleships and the main battery on several classes of armoured cruisers.

The gun was officially designated as “Type 41” from the 41st year of the reign of Emperor Meiji on 25 December 1908. It was further re-designated in centimeters on 5 October 1917 as part of the standardization process for the Imperial Japanese Navy converting to the metric system.

The Type 41 6 in gun fired a 100 lb shell with either an armour piercing, high explosive or general purpose warhead. An anti-submarine shell of 113 lb was developed and in service from 1943. 

Surviving examples

 * On board Japanese battleship Mikasa, Yokosuka, Japan
 * A coast defence gun at Fort Desoto, Florida, USA.
 * A Mk III gun and shield from HMS Calypso at Fort Nelson, Portsmouth, UK