The mechanical properties of ASTM A508 Class 2 pressure vessel steel quenched and tempered to simulate the effects of irradiation have been measured. The tensile, Charpy impact, fracture toughness, and crack arrest properties were measured as a function of temperature. The fracture toughness was measured using 1T, 2T, and 4T compact specimens. The maximum dimensions of the 4T specimens exceeded the test cylinder thickness, so compound specimens were successfully fabricated by electron-beam welding arms to the material. Compact crack arrest specimens were used to determine the arrest toughness. Two sizes of specimens were tested: 150 by 150 by 32 mm and 75 by 75 by 25 mm. The larger specimens used a brittle weld bead and notch as the crack starter. Two different notches (blunt and fatigue precracked) were used with the smaller specimens. The blunt notch was not successful, but the fatigue-precracked specimens provided valid data without the need for warm prestressing. The results from the small fatigue-precracked specimens were consistent with the data from the larger weld-embrittled specimens.