The Holland 1, a British submarine, recovered from an underwater marine site after 70 years, was found to have suffered little corrosion. The vessel is described: steel hull; steel and wrought iron superstructure; cast iron flanges; zinc, lead and copper alloys were used in other parts. Its corrosion state is discussed with reference to factors affecting corrosion rates in aerated sea water. The factor responsible for the low corrosion rate of the submarine is the general coverage by calcium carbonate scale which appears to have been biogenically as a result of anaerobic bacterial activity.