| BL 18-Inch Mk1 | |
|---|---|
 An 18-inch gun fitted to HMS Furious (47) in a single-gun turret (1917) | |
| Type | Naval gun |
| Place of origin | United Kingdom |
| Service history | |
| In service | 1918–1947 |
| Used by | Royal Navy |
| Wars | World War I |
| Production history | |
| Designer | Elswick Ordnance Company |
| Designed | 1915–1916 |
| Manufacturer | Elswick Ordnance Company |
| Produced | 1916–1920 |
| No. built | 3 |
| Specifications | |
| Mass | 149 long tons (151 t) |
| Length | 62 ft (18.9 m) |
| Barrel length | 60 ft (18.3 m) (L/39) |
| Shell weight | 3,320 lb (1,510 kg) |
| Caliber | 18 in (45.72 cm) |
| Breech | Welin breech block |
| Recoil | hydro-pneumatic |
| Elevation | -3° to +30° on Furious, +22° to + 45°, Lord Clive class |
| Traverse | 10° |
| Muzzle velocity | 2,420 ft/s (740 m/s) |
| Effective firing range | 31,400 yd (28,700 m) |
| Maximum firing range | 40,500 yd (37,000 m) |
| Filling weight | 243 lb (110 kg) |
The BL 18-inch Mk I naval gun was a breech-loading naval rifle used by the Royal Navy during World War I. It was the largest and heaviest gun ever used by the British.[1] Only the Second-World-War Japanese 46 cm/45 Type 94 had a larger calibre, 18.1 inches (46 cm), but it fired a lighter shell. The gun was a scaled-up version of the BL 15 inch Mk I naval gun and was developed to equip the "large light cruiser" (a form of battlecruiser) Furious. Its barrel length of 60 ft (18 m) was just 40 calibres, slightly limiting its muzzle velocity.
Only three guns were built, but they did not see combat with Furious before they were removed from her and transferred to the Lord Clive-class monitors General Wolfe and Lord Clive for coast-bombardment duties. Only 85 rounds were fired in combat operations before the war ended. All three were removed from service in 1920 and served as proving guns for cordite tests. Two were scrapped in 1933 and the last one survived until it was scrapped in 1947.
- ^ Hodges, p. 83