| Name: | M 3 |
| Type: | Submarine Monitor |
| Keel: | 08/12/1916 |
| Launched: | 19/10/1918 |
| Completed: | 14/07/1920 |
| Builder: | Armstrong, Whitworth & Co |
| Yard: | High Walker |
| Yard Number: | 911 |
| Dimensions: | 1600disp surf, 1950disp subm, 290.0 x 24.7 x 15.75ft |
| Engines: | 2 x Oil engines, 2400bhp and 2 x Electric motors, 1600hp |
| Engines by: | Possibly by Vickers Ltd, Barrow |
| Propulsion: | 2 x Screws, 9.5knots |
| Construction: | Steel |
| Armament: | 1 x 12.0ins, 1 x 3.0ins AA guns; 4 x 12.0ins bow torpedoes |
| History: | |
| 14/07/1920 | British Royal Navy |
| 13/04/1932 | Broken up |
| Comments: | Laid down as a K class submarine, to be named K20 |
| 1917: Renamed M3 | |
| Main gun loaded on the surface but fired when all but the muzzle submerged | |
| 1928: Guns removed and converted to a minelayer | |
| 13/04/1932: Arrived at Newport for breaking up by J Cashmore |
Above photo as original monitor configuration is courtesy of Janice M Mackenzie
Above photo as original monitor configuration is courtesy of Jim Bryce
Above photo as original monitor configuration is courtesy of Photoship
Above photo as converted to a minelayer is courtesy of Photoship
Above photo as converted to a minelayer is courtesy of Photoship