The continued growth of the offshore wind industry will depend essentially on reductions in wind energy production cost. Large cost reductions can be achieved through efficient, economic and optimised wind turbine support structures. To achieve maximum offshore wind adoption beyond 2020, significant industrial and research efforts are being made in optimised material selection and application. Fatigue and corrosion damage are the greatest challenges today in design and life estimation of wind turbine support structures. S355 steel is currently used in fabrication of most wind turbine monopile support structures. Clear understanding of their corrosion-fatigue properties and accurate steel selection will support the optimisation and economic design of extra-large wind turbines. This paper presents the fatigue crack growth test results of advanced S355 TMCP steel in air and seawater, and compares the results with studies on commonly available S355 steel. The results show that S355 TMCP steels generally offer higher fatigue damage tolerance than normalised S355 steels in air and the factor decreases and tends towards a common value with increase in stress intensity factor range. However, in seawater there is no significant difference in fatigue crack growth rates for all the S355 ferritic steels considered in this study.