| BL 13.5 inch Mk VI gun | |
| Origin: | United Kingdom |
| Type: | Naval gun |
| Is Ranged: | yes |
| Is Artillery: | yes |
| Is Uk: | yes |
| Service: | 1914–22 |
| Used By: | United Kingdom |
| Design Date: | 1909 |
| Number: | 10 |
| Part Length: | Bore 607.5inches (45 calibre) |
| Caliber: | 13.5sigfig=3NaNsigfig=3 |
| Cartridge: | 1400abbr=onNaNabbr=on |
| Velocity: | 2445abbr=onNaNabbr=on |
| Max Range: | 23110yd at +20° |
| Elevation: | 0° – +20° |
The BL 13.5-inch Mk VI gun was a British heavy naval gun, originally ordered by the Ottoman Navy to equip its dreadnoughts around 1911. The one ship completed was seized by the British Government when World War I began in August 1914 and became . Only 10 guns were built, to a design similar to that of their 45-calibre BL 13.5-inch Mk V naval gun. The smaller chamber in the Mk VI gun meant that less propellant could be used which reduced muzzle velocity by and range by 630yd. Designed by Vickers, they manufactured the guns of X and Y turrets, while Elswick Ordnance Company manufactured the guns of A, B, and Q turrets.