Improvements made since the original Dreadnought meant that they ran significantly quieter under main power, and also had a Paxman diesel-electric generator that could be used for silent running.

According to former head of the Royal Corps of Naval Constructors R.J. Daniel, when US Admiral Hyman G. Rickover, widely regarded as the father of the nuclear submarine, initially learned of the proposed rafting system for the Valiant class, (in which ship's machinery is acoustically isolated from the hull by padding known as "rafts"), he was dismissive of the concept, with the result that the Royal Navy gained an advantage in submarine silencing that the United States Navy did not introduce until considerably later.

[1] The Valiants were primarily used in the anti-submarine role, important during the Cold War.

In 1967 Valiant set a Royal Navy (RN) record of sailing 12,000 miles (19,312 km) submerged in twenty-eight days, from Singapore to the UK.

Both boats received a number of refits, including the capability to use the Harpoon missile.