BL 15-inch howitzer Mk I
In action at Englebelmer Wood, Somme, 7 August 1916
Type	Heavy siege howitzer
Place of origin	United Kingdom
Service history
In service	1915–1918
Used by	British Empire
Wars	World War I
Production history
Designer	Coventry Ordnance Works[1]
Designed	1914
Manufacturer	Coventry Ordnance Works
No. built	12
Variants	Mk I
Specifications
Mass	94 tons
Shell	HE 1,450 lb (657.7 kg)[2]
Calibre	15 inches (381.0 mm)
Breech	Welin interrupted screw
Recoil	Hydro-spring 31 inches (790 mm) constant[3]
Carriage	siege carriage
Muzzle velocity	1,117 ft/s (340 m/s)[3]
Maximum firing range	10,800 yd (9,900 m)[3]

The Ordnance BL 15-inch howitzer was developed by the Coventry Ordnance Works late in 1914 in response to the success of its design of the 9.2-inch siege howitzer.

The howitzer was cumbersome to deploy, since it was transported in several sections by giant Foster-Daimler tractors.

The weapon was operated by Royal Marine Artillery detachments of the Naval Brigade, with one gun per battery. One gun was sent to Gallipoli but not used there. They were later transferred to the British Army. It was used at the Battle of the Somme in September 1916 and at the Battle of Passchendaele, also known as the Third Battle of Ypres, in October 1917.

It operated successfully where it was needed to destroy deep fortifications on the Western Front, but was limited by its relatively short range compared to other modern siege howitzers. The size and weight made it difficult to move and emplace. No further development occurred after the first batch of twelve, and instead Britain continued to develop and produce the 12-inch howitzer and 12-inch railway howitzer.

• 
  Rolling shell along rails, Englebelmer Wood, Battle of the Somme, September 1916
• 
  German soldier posing with unexploded shell
• 
  Shell at Royal Artillery Museum, Woolwich, London
• 
  "Granny" in action during the Third Battle of Ypres, 4 October 1917
• 
  Howitzer inspected by a British delegation in 1916
• 
  A 15-inch Howitzer being set up

• List of siege artillery

• Škoda 380 mm Model 1916 howitzer Austro-Hungarian equivalent

• Dale Clarke, British Artillery 1914–1919. Heavy Artillery. Osprey Publishing, Oxford UK, 2005
• I.V. Hogg & L.F. Thurston, British Artillery Weapons & Ammunition 1914–1918. London: Ian Allan, 1972. ISBN 978-0-7110-0381-1
• Winston S. Churchill. The World Crisis, Part 2, 1915. (New York: Rosetta Books, 2013), Kindle.
• Film clip showing Royal Marine Artillery crew loading and firing the howitzer during the Battle of the Somme
• BL 15 inch Siege Howitzer at Landships