Analysis of corrosion products from the recovered remains of the USS Monitor has established the nature of the primary products that formed under the protective concretion cover and the rate of conversion into alteration products that characterise the excavated artefacts. Concentration profiles of chloride, pH and corrosion potentials at the metal surfaces of the 120 tonne (109 tonne) turret, the Ericsson engine and condenser have shown that in-situ treatment confers lasting benefits on wrought iron objects. The relative efficacy of storage in sodium hydroxide solutions and impressed current systems are reviewed.