NZAR ID 27, ARM TYPE: . Draft date (V1) 9 August 2012, Compiled by John Osborne AA DTT PhD FSG, Pattern: GR3 caliber 4.52”. Introduced: NZ July 1845. Withdrawn: 1890s

Specifications; Maker: Various. Caliber: 4.52”. Model: GR3 & GR4. Barrel: 12.5” long, smooth bore, chambered, weighs 105 pounds, Engraved with the cypher of King George III 1760‐1820. Base: hard wood with iron fittings and wooden quoin, weight of base about 75 pounds.

The Coehorn Mortar was introduced into British service from c1715 caliber 4.62” up to 1764 and caliber 4.52” post 1764. The Coehorn Mortar went through some minor changes over the years. A gunners quadrant was used to establish angle of fire, originally the barrel was fixed in the wooden block base to fire at 45 degrees to give maximum range about 800 yards, the earth was dug out under the rear of the base to increase the barrel angle, therefore giving a higher trajectory and reducing the range. To load a pre weighed black powder charge in a flannel bag was placed in the breech chamber, a 4.4” diameter bomb which weighed about 7½ pounds and fitted with an adjustable length fuse and a wooden sabot was attached to facilitate the alignment of the fuse to contact with the propellant charge. The vent and flash pan were filled with fine black powder which when ready to fire was ignited by a burning slow match held in a linstock. From about 1840 the Royal in Australia modified the base block, cut out the section under the barrel and by using a quoin (wedge) the barrel elevation could be adjusted to fire from 5 to 85 degrees. Below Coehorn mortars in use from c1715 on.

King George 1st 1715‐1727 King George 2nd 1727‐1760 King George 3rd 1760‐1820 King George 4th 1820‐1830

New Zealand Service In July 1845 an 11 man detachment of Ex Royal Artillery gunners raised in Australia led by Lt Wilmot and Sgt Kerr arrived in New Zealand with 2 x 4 ½” Coehorn Mortars, 2 x 6pdr brass field guns and 200 6pdr war rockets and 2 launching tubes. Lt Wilmot directed the mortar battery at the Battle of Ruapekapeka 31 December 1845 to 11 January 1846. The ordnance comprised three naval 32‐pounders, one 18‐ pounder, two 12‐pounder howitzers, one 6‐pounder brass gun, two 6pdr rocket‐tubes and four mortars (believed to be 2 x 4½ “ Coehorn Mortars & 2 x 5 ½” Mann Mortars) the mortar battery was situated 350 yards from the Pa. In his report to Governor Grey Col Despard commanding the troops stated ‐ great praise was due to Lt Wilmot who directed the mortar battery. The Coehorn Mortars continued to be used in the Hutt Wars of 1846 & 47 & were used to great effect in several battles during the NZ Land Wars 1860 – 72. The New Zealand Government purchased more 4 ½ “ Coehorn Mortars & 11 were listed in the 1869 return of arms & even as late as 1885 2 x 4 ½” Coehorn mortars were on issue to the Artillery in Napier & 2 on issue to the Armed Constabulary Field Force in Taranaki & 7 in store Auckland.

Left image; 3 Coehorn Mortars at Fort Britomart Auckland c1860s. Center; a Coehorn Mortar with bomb shells on Sabots at the Battle of Gate Pa April 1864. Right; rear view of a full size replica 4 ½” Coehorn mortar on its wood base, patterned from a NZ issued GR3 made by J&H King, London, 1814.

The 4½” Coehorn mortars were eventually distributed to NZ Museums, the National Army Museum has two a GR3 an GR4. Several replica full size Coehorn mortars cast in gunmetal (tin copper alloy) in Napier, NZ, made to the original specifications with quoins, are still being used in NZ to fire gun salutes on special occasions and by NZ reenactment groups for displays and recreational target shooting.

Acknowledgements and special thanks to: NZ National Army Museum, Trustees of two NZ 4 ½” Coehorn Mortars. www.armymuseum.co.nz The History of Coehorn Mortars and Shrapnel Shells and their use by Police in NZ 1846 – 1886, by John Osborne 1990. Armstrong and Coehorn Affair, by Trevor Belcher and John Osborne 1990. Research continuing.