A description is given of the examination of an 18th century cannon in an advanced state of deterioration due to the action of a marine environment. A yellow liquid of low pH, containing chloride, exuded from the piece. The corrosion was graphitic, although showing different characteristics from other cases reported in the literature. The main corrosion product was akageneite (FeO(OH)) with a skeleton of graphite flakes. Metallographic examination of the corrosion front showed an irregular interface due to selective corrosion of ferrite rather than cementite in both pearlite and ledeburite. Some procedures used in the restoration of ferrous archeological specimens are discussed. In the present case, hydrogen reduction treatment is recommended or, failing that, electrolysis at low current density. -- AATA