The C-class boats of the 1907–08 and subsequent Naval Programmes were modified to improve their speed, both above and below the surface. The submarine had a length of 142feet overall, a beam of 13feet and a mean draft of 11feet. They displaced 290LT on the surface and 320LT submerged. The C-class submarines had a crew of two officers and fourteen ratings.[1]
For surface running, the boats were powered by a single 12-cylinder[2] 6000NaN0 Vickers petrol engine that drove one propeller shaft. When submerged the propeller was driven by a 300hp electric motor.[1] They could reach 13kn on the surface and underwater. On the surface, the C class had a range of 910nmi at .[3]
The boats were armed with two 18-inch (45 cm) torpedo tubes in the bow. They could carry a pair of reload torpedoes, but generally did not as they would have to remove an equal weight of fuel in compensation.[4]
C25 was built by Vickers at Barrow and was commissioned on 28 May 1909.
While on patrol 15miles east of Orford Ness on 6 July 1918, C25 was attacked by five German seaplanes returning from a raid on Lowestoft. Attacking out of the sun, C25 was hit by their machine guns before it could use its single Lewis gun in defence. The commanding officer, Lieutenant David Bell and two of the lookouts on the conning tower were killed outright, the fourth man present was mortally wounded. While the seaplanes continued their attack, the crew tried to drag him inside delaying the dive and then one of the bodies slid across the hull, their leg stopping the hatch from being closed. Two more men were killed trying to push the body clear and in desperation the leg was cut off with a hacksaw. By this point German machine gun fire had punctured the hull and damaged the motors. An E-class submarine arrived in the area and drove off the German aircraft with its deck gun and then took C25 under tow.[5] The holes in the pressure hull were plugged by clothes, and was able to tow C25. The seaplanes returned re-armed and ready to attack again, but they were driven off by the arrival of a destroyer .[6] [7]
HMS C25 was sold on 5 December 1921.