The paper gives an outline of the non-destructive evaluation (NDE) methods currently being pursued at the Admiralty Marine Technology Establishment, Dunfermline, Scotland. The methods are being used to locate and characterise fatigue cracks in high yield strength welded steel structures. The techniques have been applied principally to large fatigue models (5' and 9' diameter) as part of a comprehensive fatigue programme, with back-up work on large T-butt welded "type test" specimens. Results are presented which illustrate the progress made with each technique in detecting and sizing fatigue cracks in welded structures. An indication of the accuracy and reproducibility is given with particular reference to ultrasonic diffraction and ACPD techniques.