The Royal Navy eventually decided that a submarine did not need to match a battle fleet at maximum speed throughout an engagement. It needed enough speed and endurance to deploy with the fleet, reach its station, and support normal cruising operations. Supercharged diesel-electric River-class boats accepted a 22-knot maximum in exchange for a more practical balance of pace and range. Their later service demonstrated the value of that compromise: Thames was lost off Norway, Clyde supplied Malta, and Clyde and Severn operated in the Far East. The class preserved the fleet-submarine idea while abandoning the K class's oil-fired boilers and extreme speed requirement.
Chapter · 48:59-52:58
The River class revised the fleet-submarine requirement
The River class traded the K class's maximum speed for useful range and enough pace to deploy and cruise with the fleet.