6-inch gun M1917

L/45
Design
First produced by Vickers in 1899 the Mk VII naval gun was a typical British built-up gun of the period constructed of steel with a central rifled tube reinforced with braided wire wound around the liner and a protective outer jacket. The Mk VII was a breech-loaded design with a Welin interrupted screw breech and used separate-loading, s and projectiles.
The Mk VII was fairly conventional for its time and most combatants during the First World War had similar conversions of naval guns such as the German 15 cm Ring Kanone L/30 or the French Canon de 155 L modele 1916. The barrels were mounted on a simple steel box trail carriages with two steel wheels, a hydro-pneumatic recoil mechanism, and no gun shield. The recoil mechanism didn't absorb all of the recoil so set of wooden ramps were placed behind the wheels and when the gun fired the wheels rolled up the ramp and the gun was returned to position by gravity. A drawback of this system was the gun had to be re-aimed each time which lowered the rate of fire. The carriages had an opening behind the breech to allow high angles of elevation.
To facilitate towing on soft ground the wheels were often fitted with patented by the Italian major Crispino Bonagente. These consisted of rectangular plates connected with elastic links and are visible in many photographs of World War I artillery from all of the combatants. Due to the weight of the gun, it could not be towed by a horse team and had to be towed by a traction engine or artillery tractor instead.
World War I
The Mk VII was first used as a field gun in France in 1915. It was initially mounted on an improvised rectangular-frame field carriage designed by Admiral Percy Scott. The carriage was based on a design he had improvised for the 4.7-inch gun in the Second Boer War. It was a successful carriage, except that it limited the elevation and range. A better carriage which allowed elevation to +22°, the Mk II, was introduced early in 1916. This was followed by Mk III, V and VI carriages which allowed up to +38. The gun was operated by the Royal Garrison Artillery in batteries of four, as were all the larger field guns in World War I.
American production
Since the British were facing a shortage of materials, labor and manufacturing capacity during the First World War a version of the Mk VII was produced in the United States for use by the British Army as the BL 6-inch Mk VIII gun. When the United States entered the First World War it also had a need for long-range heavy artillery so guns produced for the US Army were given the designation M1917. The American M1917 was based on the BL 6-inch Mk VIII naval gun which was a variant of the Mk VII whose breech opened to the left instead of the right. Since Mk VIII/VII guns were used in twin gun turrets aboard Royal Navy Cruisers the breeches opened in opposite directions to eliminate interference and make loading easier. An unknown number were delivered for British and American use during the First World War.
The main differences between the British built Mk VII and American built M1917 were:
* Since the M1917 was based on the British Mk VIII naval gun their breech opened to the left while the British Mk VII opened to the right.
* The British Mk VII gun had two recoil cylinders to the sides and rear of the barrel. The M1917 had its recoil cylinders under the front of the barrel.
* In British service, the American made M1917 was designated BL 6-inch Mk VIII to denote that it was a variant of the Mk VIII naval gun instead of the Mk VII.
*Differences in the design of the gun carriage to accommodate the recoil systems.
World War II
Between the wars, the United States modernized the M1917 by fitting pneumatic tires to allow the guns to be towed at higher speeds. The majority of guns were assigned to coastal artillery batteries protecting the Panama Canal Zone. The guns were anchored in the center of either crescent or circular shaped concrete Panama mounts which compensated for the limited on carriage traverse of the M1917. Before the war, the US Army declared the guns obsolete and when the United States entered the war in 1941 the guns were removed from service. 99 guns were sold to Brazil where they were used as Coastal Artillery until the 1960's when they were retired from service.
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