The paper describes improiements in pulse systems of ultrasonic flaw detection in three fields: (1) A mode changer (to change longitudinal waves to shear waves) which is made of heavy material in the form of a laminated assembly which gives better efficiency and better discrimination than the usual device. (2) Damping, loading and circuitry for piezo-electric crystals to give improved discrimination and to reduce the adverse effects of rough surfaces. Additional monitoring means are described which assess and display the extent of the adverse effects of the rough surfaces. (3) Devices enabling beams of mechanical waves to be steered from chosen sites to search for flaws.