The Cambridge University Department of Geodesy and Geophysics pioneered the development of radio sonobuoys which could be used from a single ship to study the structure of the submarine crust. Contemporaneous marine seismic research, mainly in the USA, by contrast used more expensive techniques requiring the use of two ships. For nearly three decades from the early 1950s several generations of Cambridge sonobuoys were used as the primary tool to study the structure of the oceanic crust and the adjacent continental margins by seismic refraction methods, until superseded by ocean bottom seismographs. An early result was to confirm the ubiquity across the world of relatively thin (compared to continental crust), probably volcanic oceanic crust. This in turn underpinned the subsequent recognition of seafloor spreading and plate tectonics.