High-strength steels are widely used in marine engineering; however, they suffer from the risks of corrosion, hydrogen permeation, and stress corrosion cracking (SCC) in wet–dry cyclic marine environments. In this study, the corrosion, hydrogen permeation, and SCC behaviours of AISI 4135 steel in the tidal zone were investigated using electrochemical corrosion, electrochemical hydrogen permeation, and slow strain rate tests, respectively, via field exposure. The results showed that the AISI 4135 steel sample placed at the high tide level had high SCC susceptibility because of severe pitting corrosion and hydrogen permeation, whereas the steel samples placed at the middle and low tide levels had low SCC susceptibilities. The dry/wet time ratio was crucial in determining the SCC behaviour and mechanism of the steel in the tidal zone. With increasing time ratio, the SCC mechanism changed from micro-void coalescence control to localised anodic dissolution and hydrogen embrittlement in tandem.