[en] Three essentially identical steel pressure vessel models 254 mm (10 in.) in diameter, 38 mm (1.5 in.) in wall thickness, and containing long, through-the-wall machined and sharpened axial flaws were tested to failure at different test temperatures. The principal objective of the tests was to assess the adequacy of a particular design configuration for additional larger-scale tests. The goal of achieving both arrest and nonarrest of a rapidly propagating crack in a pressurized vessel configuration was met, with qualifications. The results suggest that design modifications should be considered for further testing. The vessels consisted of cylindrical sections joined together by electron-beam welding, with the sections having substantially different toughnesses as a result of different heat treatments. Crack extension initiated in relatively brittle sections, and the cracks extended both stably and unstably, depending on the test temperature, toward the tougher sections and then arrested in two of the models. Charpy V impact specimens and both slow-bend and dynamic precracked Charpy V specimens were used extensively for material characterization