Once the most pressing needs had been filled by the Marks I to V 8inch howitzers, attention was turned to making a more efficient design, and in August 1915 Vickers were requested to produce a new 8inch howitzer design. The first 8inch Mark VI howitzer came off the assembly line on 1 March 1916. The design was quite simple: a box trail with a top carriage permitting 4° of traverse to each side, a cradle with a hydro–pneumatic recoil system, and permitting 50° of elevation, and traction-engine wheels. The breech was faster and more modern. This combination resulted in a maximum range of 9825 metres, plus a total weight of 8tons, 10cwt, 2qr and 13lb (some five tons less than the previous marks). When compared to earlier versions it had a better recoil system, but still needed ramps under its wheels for controlling the rest of its considerable recoil.
The problem with the Mark VI was its mediocre range, and soon it became obvious that range was a crucial factor. This prompted a redesign resulting, in June 1916, in the Mk VII, which was almost identical to the predecessor, except that the barrel had been lengthened to 17.3 calibres. Several small re-designs followed, eventually resulting in the Mark VIII 8inch howitzer. This could hurl a 200lb (90.8kg) shell up to a range of 12,300 yards (11,240m).
The breech system was of the Asbury interrupted screw type. The howitzer could be towed either by tractor or horse. (A limber needed to be used for both towing methods.) The wheels were 30cm wide and had a 170cm diameter. It was indeed a heavy howitzer: the weight of the barrel and breech together was 2.9tons and just the screw part of the breech weighed 174kg. Rate of fire was only about 1 shot per minute, due in part to the weight of the barrel, which demanded lowering the barrel to zero for reloading. The 8inch Howitzer used bagged ammunition: projectile, propellant bags and primer were loaded separately - no cartridge case was used. There were four sizes of propellant charge, each giving different ranges. This type was used by the British in the early years of WW2, and it was not declared obsolete until 1943.
The gun was also used by the French Army, and the US Army, and also produced in the USA. Just eight days after the American declaration of war with Germany (passed by their Congress on 4th April 1917), 80 8inch howitzers were ordered from the Midvale Steel and Ordnance Co., at Nicetown, Pennsylvania, a firm that was already manufacturing them under British contracts at the time. Production rolled so fast that the first completed unit was test fired on December 13, 1917. The total order was eventually increased to 195; 146 were completed and accepted by November 14, 1918; 96 of these were shipped overseas.
During the Winter War of 1939-40 Finland, in its desperation, bought 32 8inch Howitzers from the USA, but they arrived too late for that war. They came cheap, but were in desperate need of maintenance before they could be deployed. They were put to good use in the Continuation War 1941-44, though. The Finns liked the howitzer, which they found very reliable. After WW2 the remaining howitzers were stored in case of war until the late 60s.
The gun below is an American-made Mk VI (although it does say 'Vickers' on the breech, it is clearly stamped 'M.S. & O. Co' for Midvale Steel and Ordnance Co.), one of those sold by the USA to Finland, and used by the Finns in the War 1941-44. It is displayed outside the War Museum in Helsinki, Finland:
D Clarke & B Delf, British Artillery 1914-19, Heavy Artillery, 2005, Osprey Publishing Ltd, Great Britain.
Strelets make a gun and crew, in 1/72 plastic. Matador Models make a 1/76 white metal kit. IT Miniatures make a 1/72 white metal kit of an 8in howitzer, but it is not stated which Mark it is, so it may not represent a Mark VI to VIII.