Extensive F-region ionospheric disturbances were recorded at the New Zealand ionospheric stations at Rarotonga, Christchurch, and Campbell Island followingthe Johnston Island nuclear explo5ions. From these records, as well as from magnetic recordings made at adjacent stations, the characteristics of the ionospheric movements, and of the gaseous wave which generated them have been deduced. The ga5eous wave appears to be a surface wave with velocity greater than that of sound and it has some of the characteristics of a normal shock wave.