|BL 15-inch howitzer Mk I|
|Type||Heavy siege howitzer|
|Place of origin||United Kingdom|
|Used by||British Empire|
|Wars||World War I|
|Designer||Coventry Ordnance Works|
|Manufacturer||Coventry Ordnance Works|
|Shell||HE 1,450 lb (657.7 kg)|
|Calibre||15 inches (381.0 mm)|
|Breech||Welin interrupted screw|
|Recoil||Hydro-spring 31 inches (790 mm) constant|
|Muzzle velocity||1,117 ft/s (340 m/s)|
|Maximum firing range||10,795 yd (9,871 m)|
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.
"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