Nomenclature: Ordnance QF 4.5in howitzer Mark I or II on carriage field QF 4.5in howitzer Mark I
Weight of Equipment: 1ton, 6cwt, 3qr, 14lb
Ammunition type: separate loading QF
Calibre: 4.5in
Projectile Type & Weight: HE, 35lb; shrapnel, smaoke, star shell, incendiary, gas
Maximum Range: 7300 yards

After all the unexpected setbacks suffered by the British in the Boer War, gunmakers were asked to submit new designs for a Field Howitzer, and the one done by the Coventry Ordnance Works was chosen. The new QF (Quick Fire) howitzer entered service in 1909, replacing the old 5inch BL howitzer. In 1914 the British 4.5inch (114mm) Field Howitzer was perhaps the best piece in its class in the world. (It's only competitor then was the German 98/09, which had comparable performance in all fields but one: the British piece out-ranged it. The British gun also had a slightly better elevation capability.) It weighed 1.368kg deployed, and fired a 15.9kg HE shell to a maximum range of 7.5km. The design was simple and reliable. It had a box trail which allowed for 45° elevation, and it had 3° traverse to the left and right, and a steel shield which was sloped back to such a degree that a special hatch had to be made for the dial sight. Recoil was controlled by a so called variable-length hydro-spring system.

Over three thousand had been built by the end of the Great War; New Zealand, Canada and Australia all received some. Also, in 1916 400 were sent to a hard-pressed Russia. It was the first British field piece to use a sliding block breech mechanism, and certain modifications were made in 1917 to the block, to rectify a tendency to crack around the angles of the mortise, which could lead to the block blowing out. This version was known as the Mk 2. At the same time, the rifling was simplified to a uniform twist which was just as good as the "increasing-twist" employed before, but a lot easier to produce. During the 1930s the old spoked artillery wheels (Wheel 2nd Class C No45) were replaced by pneumatic tyres in line with the mechanization of the Royal Artillery. The howitzer actually stayed in service until 1944 as a training weapon, but didn't see action after the 25 pounder had replaced both it and the 18 pounder in field regiments.

The 4.5inch Howitzer below has been photograped by Knut Erik Hagen:

The photos below have been taken by P Radley, and show the gun that is on display at the Royal Artillery Museum, London, England. (It is seldom you see guns kept in this really immaculate condition. I would say that it is fully functional, and in condition to fire a round in a couple of minutes. Well done, Royal Artillery Museum!)

The 4.5inch Howitzer below has been photograped by Mike Casale. It is the modernized 30-ies version, with pneumatic tyres, but beside that, and the big aperture cut in the shield, there is little difference between this gun and the ones employed in WW1:

Matador Models make a 1/76 scale white metal kit of this gun, reviewed here.
SHQ also make a white metal 1/76 scale kit, that comes with both spoked and pneumatic wheels.
Early War Miniatures make a white metal 1/72 scale kit.
HäT Industrie make a plastic 1/72 kit, set number 8243, that has four guns in the box, but no limber (here is PSR's review).
W^D Models has a resin and white metal, highly detailed kit available in 4mm:foot scale.

D Clarke & b Delf, British Artillery 1914-19 Field Army Artillery, 2004, Osprey Publishing Ltd, England.