|Builder:||Vickers Armstrong, Barrow-in-Furness|
|Laid down:||15 March 1910|
|Commissioned:||30 August 1911|
|Fate:||Sunk 12 March 1918|
|Class & type:||D class submarine|
|Displacement:||Surfaced= 483 tons / Submerged= 595 tons|
|Length:||163.0 ft (49.7 m) (oa)|
|Beam:||13.6 ft (4.1 m) (oa)|
|Propulsion:||550hp electric 1750hp diesel twin screws|
|Speed:||Surfaced=14.0 kts / Dived= 10.0 (design) 9.0 (service)|
|Range:||Surface= 2500nm at 10 kts / Submerged=45nm at 5knots|
|Armament:||3x18 in (46 cm) torpedo tubes (2 forward, one aft, 6 torpedoes) / 1x12 pdr (76 mm) QF gun|
D3 met her fate on 12 March 1918. She was mistakenly bombed and sunk by a French airship AT-0 off Fecamp in the English Channel and lost with all hands. AT-0 was patrolling when at 1420 a vessel was spotted to her north east. The airship drew close for recognition purposes and according to her commander, Lieutenant (RCN) William McKinstry Heriot-Maitland-Dougall the submarine fired rockets at her. Four 52-kg bombs were dropped by the airship. The submarine disappeared but several minutes later men were seen in the water. Attempts were made by the airship to rescue the men but it proved too difficult. The airship withdrew to seek help but all the men had drowned by the time it arrived. It is clear that D3 was the victim of a serious identification error on the part of the French airship, with identification rockets being mistaken for aggressive gunfire.
- Fitzsimons, Bernard. Illustrated Encyclopedia of 20th Century Weapons and Warfare (London: Phoebus, 1978), Volume 7, p.674, "D.1".
- Fitzsimons, p.674.
- Innes McCartney (2002). Lost Patrols: Submarine Wrecks of the English Channel.
- Submarines, war beneath the waves, from 1776 to the present day, By Robert Hutchinson
- The Royal Navy Submarine Service, A Centennial History, by Antony Preston