The results of hydrogen-induced cracking, hydrogen stress corrosion cracking (HSCC) and HSCC tests under cathodic protection obtained on the normalised medium/high strength steels for marine applications, ASA 56, ASA F56 and ASA F60, are reported. Fatigue precracked WOL specimens were loaded at room temperature and simultaneously exposed to synthetic seawater, saturated or not by hydrogen sulphide (H2S) and at two initial pH values (pH = 1; pH = 3). Here indications are given on the types of mechanisms controlling the damaging, the comparison of the values of the crack propagation threshold stress intensity factor in air and in corrosive media, the influence of the presence of H2S, the role of inclusions and of their plane's orientation, the relationship between the damaging phenomena, the effect of the cathodic protection.