In some recent impact tests in which thin walled square tubes were loaded axially to produce large scale buckling of the walls, a difference occurred between the behaviour at high speeds and that at low speeds. The tubes, standing on an anvil, were struck by a falling steel tup which was guided to strike the tubes approximately axially. At the higher speeds damage was confined to the impact end of the tube, with a short wavelength buckle adjacent to the end and longer waves farther from the end. At lower speeds damage occurred at either end, or, jn many cases, in the central region of the tube. The wavelengths in these low speed tests were longer than those occurring at high speeds. These two types of behaviour are illustrated on Fig. 1.