fitted with anechoic tiles captured from the Germans. The boat had a reserve buoyancy of 28%, enough to remain afloat with any single compartment flooded, a figure more than two and a half times greater than that of the Type XXVI. S-99 had a test depth of and a design depth of . In service, she proved to be maneuverable and was very noisy at full speed. The submarine was primarily powered by a Walter HTP turbine that drove a single propeller shaft using steam generated when highly concentrated hydrogen peroxide was sprayed onto a layer of activated charcoal to produce high-pressure steam and oxygen at a temperature of . This passed into a combustion chamber into which kerosene was injected. The resulting combustion converted the oxygen into carbon dioxide and carbon monoxide and further increased the mixture's temperature and pressure. Water was then added to the mixture to reduce the temperature down to about , double the volume of the steam and convert the supersaturated steam into saturated steam better suited for powering a geared steam turbine. The steam/gas mixture was passed through a condenser to recover the water while the combustion gases were exhausted into the ocean. S-99s turbine could generate in shallow water, but only at depths of because the pressure of the deeper water created more back pressure which reduced the turbine's efficiency. The turbine gave the boat a submerged speed in excess of . S-99 was also provided with a diesel-electric system that consisted of a 8Ch-23/30 diesel engine and a PG-100 electric motor for cruising. An additional electric motor was intended for slow speeds underwater and could be powered by either the 112 Type 26-SU battery cells or a DG-17 diesel generator. The boat was fitted with a folding snorkel to allow the diesel engines to operate while underwater. The submarine's maximum speed on the surface was and she had a range of at maximum speed on the Walter turbine and at . Using her diesel-electric system on the surface gave S-99 a range of at ; using her snorkel reduced it to at . Using just the electric motor underwater, the submarine had a range of at . She had internal fuel tanks for of diesel fuel and of kerosene. Plastic bladders between the pressure hull and the outer hull held of very expensive hydrogen peroxide. S-99 carried enough supplies for 45 days