 An example was that "Tireless" had had a small radioactive coolant leak for eight days in February 2013.As a refinement of the preceding Swiftsure-class, the design of the "Trafalgar"-class bears some similarity, including its internal layout and the Rolls-Royce PWR1 Core 3.However some improvements over the "Swiftsure" class include its reduced acoustic signature, thanks to the hull being covered in anechoic tiles which are designed to absorb sound rather than reflect it, making the boats quieter and more difficult to detect with active sonar.