Importation of liquefied natural gas (LNG) by ocean-going tankers is one short-term solution to the energy crisis. One of the promising candidate materials for the LNG tankage on these vessels is a specially heat treated 5 percent nickel alloy steel according to ASTM Specification for Pressure Vessel Plates, Five Percent Nickel Alloy Steel, Specially Heat Treated (A 645-74). Fatigue data were developed to determine the growth rates of partial-thickness cracks (PTC) as a function of temperature, stress ratio, and fundamental parameters pertinent to spectrum loading. Constant amplitude PTC growth rate was reduced as the test temperature was lowered, accelerated as the stress ratio was increased, and shown to be approximately equivalent to through-thickness crack growth rates available in the literature. Results of variable amplitude tests showed a significant crack growth retardation effect. These data plus a typical ship spectrum loading histogram were programmed into a computer to make in-service fatigue life predictions. The performance of this computer program was checked against an actual spectrum loaded specimen.