The subcommittee for Effective Utilization of Yield Strength was established under the Materials Division of the Pressure Vessel Research Committee of the Welding Research Council to study the effects of strain hardening and the yield strength to tensile strength ratio on the various failure modes of pressure vessels. Specifically their purpose is to determine if high-strength steels can be more effectively utilized in pressure vessel applications than present design criteria permit and with appropriate safety. As a part of their over-all program, a series of fatigue crack initiation tests were run using pressure vessel steels with a wide range of strain hardening exponents (0.08 to 0.36) using compact tension specimens having various geometries. Also, tests were conducted (1) to determine the effects of a single overload on initiation life, and (2) to study the life in the shadow of the notch. In addition a design approach to predict the fatigue crack initiation life was suggested.