Description
The 18-pounder was a quick-firing horse-drawn field gun designed to be towed behind a limber and six horses. The gun barrel was wire bound nickel-steel with a single-motion screw breech with a cartridge extractor. It fired a fixed round of shell and cartridge fixed together, which was known as "quick firing" in British terminology. The lower carriage comprised a single hollow steel trail fixed to the centre of the axle-tree. The limited traverse saddle supported the elevating mass and a shield. Traverse controls were on the left and elevation on the right of the saddle. Recoil was by a hydraulic buffer with telescopic running-up springs to return the barrel to its firing position.
The Equipment Committee's conditions required tangent sights (i.e. direct fire) with the option of a telescope. However, the 18-pounder entered service with rocking bar (also called "bar and drum") sights - open sights with the option of a telescope on the left and a range scale (in yards) on the right of the cradle. These arrangements also incorporated independent line of sight, meaning that the sights could remain laid on the target while the barrel was elevated or depressed. A clinometer was provided for indirect fire when the sight was aimed using a gun-arc (a refined version of the expedient devices used in South Africa) and aiming posts in line horizontally with the target.
However, in 1906 indirect fire goniometric sights were adopted, consisting of an alidade mounted on a circular scale graduated in degrees that was mounted on the shield. In 1910 the Number 3 Dial Sight, a refined version with a telescope and compass, replaced the goniometer. The rocking bar and telescope were retained for direct fire, as was the range scale on the right in spite of a clinometer being part of the Dial Sight mount.
In 1910, after three years of trials, the German Goertz panoramic sight was selected as the Number 7 Dial Sight. This, with its sight mount that again included a sight clinometer, replaced the No 3. However, resolving various issues, notably with the sight and mount carrying case mounted on the shield, meant that the Number 7 sight did not enter service until early in 1914.
Unusually for a 20th century British gun, the 18-pounder retained two man laying throughout its life, elevation (in yards) was set on a range scale on the righthand side of the cradle. The Equipment Committee had also insisted on better methods of fuze setting, important because until late in 1914 it only had time fuzed ammunition. A hand held mechanical fuze setter was developed, and in early 1914 a "fuze indicator" was introduced, this converted the range into a fuse setting.
Read more about this topic: Ordnance QF 18 Pounder
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