A dive from steam-powered surface operation normally required 30 minutes. Minimum time needed to secure the main engines, shift to battery motors and dive under emergency conditions was nearly 5 minutes, which, though better than the 15 minutes of the "Swordfish" prototype, was considered barely adequate. The boiler fires were first extinguished to prevent submerged buildup of fumes; a complicated series of hydraulics and mechanical rods and levers lowered the twin funnels away from each other to a horizontal position in wells in the superstructure as well as simultaneously closing hatches over the funnel uptakes. The main intake ventilators were likewise closed along with sea water connections for condensers and boiler feed. It was considered that with their of speed the submarines could turn and outrun almost any threat if they were attacked on the surface, dispensing with a need for a rapid dive. This perhaps just excused the fact that the fast 'crash dives' of conventional submarines were unattainable.