The work that I'm going to describe was funded by the Air Force Materials Lab from February 1972 to February 1974. It is described in an AFML report, TR- 74-80, available from the Air Force. This report describes a more practical type of problem than has been discussed so far. Our work was directed towards building an ultrasonic system to be used on aircraft in the field to detect cracks around fastener holes with the fastener in place. With this system we are able to detect cracks and locate them relative to the depth of the hole. Estimates of crack size by this method are not very accurate.