Abstract: There is described a snorkel mast for a submersible vehicle. The mast terminates at the upper end in an inverted U-shaped snorkel head pipe section closed by a butterfly valve. The butterfly valve is operated by a bell-crank lever having a float at one end and a water impact flap at the other. Operation of the bell-crank lever by water level action against the float or by water impact action on the flap if a wave washes over the top of the snorkel mast acts to close the butterfly valve. The mast carries a fairing which comprises a number of fairing elements of airfoil cross-section, vertically spaced on the mast so as to be freely rotatable thereon in water lubricated bearings. The segmented fairings on the snorkel mast maintains hydrodynamic stability during high speed turns.