The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code requires that dynamic fracture toughness data be developed for materials with specified minimum yield strengths greater than 345 MPa (50 ksi) to provide verification and utilization of the ASME specified minimum reference toughness K_IR curve. In order to qualify ASME SA508 Cl 2a pressure vessel steel [minimum yield strength equals 450 MPa (65 ksi)] per this requirement, dynamic fracture toughness tests were performed on three heats of base and heat-affected-zone (HAZ) material from both automatic and manual submerged-arc weldments. Linear elastic K_Id results were obtained at low temperatures while J-integral techniques were utilized to evaluate dynamic fracture toughness over the transition and upper shelf temperature ranges. Loading rates in terms of K were on the order of 2.2 to 4.4 × 10⁴ MPam/s (2 to 4 × 10⁴ ksiin./s). Tensile, Charpy impact, and drop weight nil ductility transition (NDT) tests were also performed. All dynamic fracture toughness values of SA508 Cl 2a base and HAZ material exceeded the ASME specified minimum reference toughness K_IR curve. Upper shelf temperature resistance curves obtained by the standard multiple-specimen J test technique, where each specimen was loaded dynamically to a specific displacement, and resistance curves obtained via specimens loaded dynamically to failure, yielded essentially identical J_Id values.