British Mortars

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Description

For a more general view of the subject please refer to our article British Artillery Equipment. The present article is dedicated to the detailed presentation of the various types of mortars used by the British Army.

British mortars were manufactured as 13-, 10-, 8-, 5 1/2-inch (royal - brass only), and 4 2/5-inch (coehorn - brass only). They could use the same shells as the howitzers. These naming references are tied to the width of the bore or the diameter of the shell — the larger pieces best match the bore diameter, the smaller pieces best fit the shell diameter. In the early 1700s, the British did produce a limited number of iron coehorn mortars, but there is no mention of these pieces in reference to the Seven Years' War (Caruana, Arms Collecting, Vol. 26, No.4). Captured British Coehorn mortars were referenced as grenade mortars by the French.

In 1753, the corresponding shell sizes were 12.75 inches, 9.75 inches, 7.75 inches, 5.54 inches, and 4.40 inches (McConnell 1988, Page 291). In general, mortars were much lighter in weight than the corresponding howitzer with the ground offering stability and support to the mortar when fired, otherwise the need for thicker metal on a carriage mount.When compared to the corresponding brass mortar, the 13-inch and 10-inch iron mortars were much bulkier pieces with greatly increased wall thicknesses (not bore lengths). With these large iron mortars, a greater gunpowder charge could be used resulting in a doubling of the range. This was not true for the 8-inch mortars where there was a minimal difference in maximum range between brass and iron mortars.

Mortars were mounted on timber beds. Iron beds had not been introduced yet. For the larger mortars, these beds were comparable to the weight of gun carriages. Exacting detail for the construction and dimensions of mortars beds is found in McConnell, but any estimate of the resulting carriage weight is often missing (1998).

Seemingly, the Coehorn mortars were intended to be used in-mass. Braddock brought 15 Coehorn mortars to Virginia in 1755, but his advance column only included three of these mortars. In 1757 and 1758, William Pitt (Secretary of State, Southern Department) shipped a total of 60 Coehorn mortars to North America for use in the campaigns against Canada.

Mortar Models

4½-in Brass Coehorn Mortar

Model Barrel
Weight
Barrel
Length
Barrel
Bore
Shell
Weight
Shell
Diameter
Charge Range
4½-in Brass Mortar 84 lbs
38.1 kg
1 ft 10 in
55.88 cm
4.52 in
11.48 cm
8.5 lbs
3.86 kg
4.40 in
11.18 cm
3 oz 12 dr 600 yards
549 m.


The coehorn mortar plus bed would weigh some 180 lbs (81.65 kg).

5½-in Brass Mortar (Royal Mortar)

The 5½-inch mortar was very light. However, its performance can be best described as erratic.

Model Barrel
Weight
Barrel
Length
Barrel
Bore
Shell
Weight
Shell
Diameter
Charge Range
5½-in Brass Mortar 140 lbs
63.5 kg
2 ft 2 in
66.04 cm
5.62 in
14.27 cm
16 lbs
7.26 kg
5.54 in
14.07 cm
8 oz 6 dr 1,000 yards
914.4 m.


The 5½-inch mortar plus bed weighed some 275 lbs (124.74 kg).

8-in Mortar

Historical correspondence often referenced British 7-inch mortars. This was a reference to shell size. All British 7-inch mortars are better referenced as 8-inch.

Model Barrel
Weight
Barrel
Length
Barrel
Bore
Shell
Weight
Shell
Diameter
Charge Range
8-in Brass Mortar 476 lbs
215.9 kg
n/a n/a 46 lbs
20.87 kg
7.75 in
19.69 cm
n/a 1,600 yards
1,463 m.
8-in Iron Mortar 896 lbs
406.4 kg
n/a n/a 46 lbs
20.87 kg
7.75 in
19.69 cm
1 lb 9 oz
0.71 kg
1,720 yards
1,572.8 m.


The 8-inch mortar bed weighed some 620 lbs (281.23 kg). Married to its bed, the 8-inch iron mortar was just over 1,500 lbs (680.4 kg).

10-in Mortar

Model Barrel
Weight
Barrel
Length
Barrel
Bore
Shell
Weight
Shell
Diameter
Charge Range
10-in Brass Mortar 1,150 lbs
561.6 kg
n/a n/a 93 lbs
42.18 kg
9.75 in
24.77 cm
n/a 1,200 yards
1,097 m.
10-in Iron Mortar 1,790 lbs
811.9 kg
n/a n/a 93 lbs
42.18 kg
9.75 in
24.77 cm
4 lb 8 oz
2.0 kg
2,536 yards
2,218 m.


The 10-inch mortar bed weighed some 1,140 lbs (517.1 kg).

13-in Mortar

In August 1757, the French captured Fort William Henry on Lake George in northern New York. Included in the materials surrendered was a store of 13-inch mortar shells, a very good fit for the French 12-inch mortars defending Québec. Montcalm and his men then returned to Canada, transporting 168 British 13-inch shells north with them ― 16.8 tons.

Model Barrel
Weight
Barrel
Length
Barrel
Bore
Shell
Weight
Shell
Diameter
Charge Range
13-in Brass Mortar 2,800 lbs
1,270 kg
n/a n/a 200 lbs
90.72 kg
12.75 in
32.39 cm
n/a 1,300 yards
1,189 m.
13-in Iron Mortar 4,030 lbs
1,828 kg
n/a n/a 200 lbs
90.72 kg
12.75 in
32.39 cm
8 lbs
3.63 kg
2,700 yards
2,469 m.


The 13-inch mortar bed weighed some 1,520 lbs (689.5 kg).

References

Adye, Ralph Willet. 1802. The Bombardier and Pocket Gunner. Printed for T. Egerton, Military Library, Whitehall. By W. Blackader, Took's Court, London. Online.

Caruana, Adrain. 1979. British Artillery Ammunition, 1780. Museum Restoration Service. Bloomfield, Ontario.

Caruana, Adrain. 1989. British Artillery Design in British Naval Armaments, ed. Robert D. Smith. Royal Armouries, Conference Proceedings 1. London.

Caruana, Adrain. 1992. Introduction: The Artillerist's Companion 1778 by T. Fortune. Museum Restoration Service. Bloomfield, Ontario.

Caruana, Adrian. Coehorn Mortar. Arms Collecting, Vol. 26, No. 4. Museum Restoration Service, Bloomfield, Ontario, Canada.

Cubbison, Douglas R. 2010. The British Defeat of the French in Pennsylvania, 1758: A Military History of the Forbes Campaign Against Fort Duquesne. McFarland & Company, Inc., Jefferson, North Carolina.

Cubbison, Douglas R. 2014. All of Canada in the Hands of the British: General Jeffery Amherst and the 1760 Campaign to Conquer New France. University of Oklahoma Press. Norman.

Cubbison, Douglas R. 2015. On Campaign Against Fort Duquesne: The Braddock and Forbes Expeditions, 1755-1758, through the Experiences of Quartermaster Sir John St. Clair. McFarland & Company, Inc., Jefferson, North Carolina.

Dawson, Dawson and Summerfield. 2007. Napoleonic Artillery, Crowood Press.

Doughty, Arthur George. 1901. The Siege of Quebec and the Battle of the Plains of Abraham; Volume 6: Appendix Part II. Dussalt & Prolux, Quebec.

Duncan, Francis. 1879. History of the Royal Artillery, Volume I, 3rd Edition. John Murray, London.

Fortune, T. 1778. The Artilleriʃt's Companion, containing the Diʃcipline, Returns, Pay, Proviʃion, &c. of the Corps, in Field, in Forts, at Sea, &c. Forward by Adrian Caruana. Museum Restoration Service, 1992. Bloomfield, Ontario.

Henry, Chris and Brian Delf. 2002. British Napoleonic Artillery 1793 - 1815 (1): Field Artillery. Osprey Publishing Ltd. Oxford.

Henry, Chris and Brian Delf. 2004. Napoleonic Naval Armaments, 1792-1815. Osprey Publishing Ltd. Oxford.

Hughes, B.P. 1969. British Smooth-Bore Artillery. Stackpole Books, Harrisburg, Pennsylvania.

Kinard, Jeff. 2007. Artillery: An Illustrated History of its Impact, ABC Clio.

Lavery, Brian. 1987. The Arming and Fitting of English Ships of War, 1600-1815. Conway Maritime Press. London.

Lavery, Brian. 1989. Carronades and Blomefield Guns: Developments in Naval Ordnance, 1778-1805. In: British Naval Armaments; Edited by Robert D. Smith. Royal Armouries, Conference Proceedings 1. London.

May R. and Embleton G. A. 1974. Wolfe's Army, Osprey Publishing, London.

McConnell, David. 1988. British Smooth-Bore Artillery: A Technological Study to Support Identification, Acquisition, Restoration. Reproduction, and Interpretation of Artillery at National Historic Parks in Canada. Minister of Supply and Services Canada. Available Online.

Meide, Chuck. 2002. The Development and Design of Brass Ordnance, Sixteenth through Nineteenth Centuries. The College of William and Mary. Online.

Muller, John. 1768. A Treatise of Artillery. John Millan, Whitehall, London. Online. (First edition is 1757, available online as well. Not identical, notable in the Introduction).

O'Callaghan, E. B. 1858. Documents Relative to the Colonial History of the State of New York: Procured in Holland, England and France. Vol. X, Weed Parsons and Company, Printers, Albany. Online. Note: Some written histories will cite these documents as O'Callaghan, but most online sources will have John Romeyn Brodhead as the author per the cover page. O'Callaghan did the editing and translations from the French.

Pargellis, Stanley 1936. Military Affairs in North America, 1748-1765. "MANA". Selected Documents from the Cumberland Papers in Windsor Castle. American Historical Association, 1936. Reprinted: Archon Books, 1969. Online.

Partridge, Mike, The Royal Regiment of Artillery, in Seven Years War Association Journal, Vol. XII No. 3

Persy, N. 1832. Elementary Treatise on the Forms of Cannon & Various Systems of Artillery. Translated for the use of the Cadets of the U.S. Military Academy from the French of Professor N. Persy of Metz. Museum Restoration Service, 1979.

Scharnhorst, Gerhard Johann David. 1787. Handbuch für Offiziere in den Andwendbaren Theilen der Kriegeswissenschaft, Hanover.

Wise, Terence and Richard Hook. 1979. Artillery Equipments of the Napoleonic Wars. Osprey Press. London.

Acknowledgments

Digby Smith for the initial version of this article

Ken Dunne for the global overhaul of the article in 2021