Ultrasonic holography has proven to be a useful and accurate tool for defect imaging and sizing in thick wall materials. The optical image formation gives a true two-dimensional cross-section of the flaw as a function of the angle at which the flaw is inspected. Recently Babcock & Wilcox participated in Oak Ridge Laboratories thermal shock program of HSST test vessels, under at EPRI contract, to attempt to define cracks induced into the vessels. The defects induced were "natural" cracks running the length of the vessel.