A technique has been developed for the accurate measurement of crack depth in thick-walled cylinders using a straight-beam ultrasonic probe. This technique has proved useful not only under laboratory conditions, but also in practical situations such as inspection of cannon tubes after firing. In the presence of multiple cracks, the measurement, recording and analysis of all the factors of fatigue crack growth can be quite complicated. To alleviate this problem a system for the rapid collection reduction, and analysis of this data by computer has been developed. The resulting measuring devices, the data acquisition system and the link to an IBM 360 computer is described. Various computer programs used to process the data and illustrating the kind of information and graphical output that can be generated are described. This includes a graphic representation of all the cracks present showing their location and depth. The importance of the rapid data analysis feature of the system to apply fracture mechanics theory for the control of the fracture process in thick walled cylinders is demonstrated.