The "Leopard" class was also fitted with an early type of hydraulic stabiliser system consisting of two fins that could be extended outside the main hull, to port and starboard, from a compartment between the two engine rooms. Gyro controlled with a relatively simple control system, they proved very effective in use. During testing every three months at sea, the ship could be easily driven into a 20°+ roll from the manual control on the bridge. Prior warning had to be given over the ship's tannoy system before testing was carried out, to allow stowage of loose items. A slight reduction in top speed was also noticed when in use.