An important class of subsurface cracks occur in nuclear power plant pressure vessels. These pressure vessels, normally made of carbon steel, are protected by a layer of weld material applied directly onto the surface, leaving a highly inhomogeneoue cladding with a rough surface and a very irregular interface. Subsurface cracks originate at the interface between the carbon steel walls of the pressure vessel and the protective cladding layer. The propagation is initially into the carbon steel and eventually into the cladding, and needs to be detected before reaching the surface (Fig. 1). The inhomogeneity of the cladding material and the irregular surfaces pose serious difficulties for ultrasonic detection. These difficulties are less critical for eddy current testing due to the fact that the layered structure of the cladding has more variation in its elastic properties than its electrical conductivity.