Koehler Depressing Carriage

The Koehler Depressing Carriage was a novel type of gun carriage invented in 1782 by Lt George Frederick Koehler of the Royal Artillery. It was devised to enable cannons to be fired at a steeply downward-facing angle and was made necessary by the peculiar circumstances that the British Army faced during the Great Siege of Gibraltar between 1779–83. The carriage saw active service during the siege, when it was used to support the British counter-bombardment of Spanish and French artillery batteries during the successful defence of Gibraltar. Its success made Koehler famous and has been commemorated in a number of different forms over the last 230 years.

During the Great Siege, the British garrison of Gibraltar faced a French and Spanish army entrenched on the low ground of the isthmus that links Gibraltar with Spain. The British controlled the high ground of the Rock of Gibraltar, which reaches a height of 411.5 metres (1,350 ft) at its north end. Although this was a major advantage for the British gunners, as it gave them an increased range and a clear view of the enemy, it also posed significant problems. Enemies close to their positions could not be targeted as existing gun carriages would not allow the amount of vertical depression required to hit such a close target. Gunners tried to deal with this by propping up the rear of the carriages, but this was a clumsy solution that fixed the guns in position. It consequently exposed them to severe danger as they had to load the guns in full view of enemy counter-fire, rather than out of sight in an embrasure or battery.

Depressing carriages had been invented before – in the 15th century, a German engineer had devised a platform for a culverin that had four wheels and could be moved in two arcs for adjusting the elevation – but Koehler found a simple and effective solution that solved both the problems of elevation and recoil. It was based on an existing garrison carriage, a type of heavy gun carriage mounted on small wheels known as trucks. Koehler split the carriage in two horizontally, joining the two parts with a hinge created with a spindle at the front. This allowed the gun to be depressed to an angle of between 20 and 70 degrees. The cannonball and powder were held in place using wadding to secure them in the bore.

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