John Crossley Swallow

John Crossley Swallow FRS (11 October 1923 – 3 December 1994) was an English oceanographer who invented the Swallow float (sometimes referred to as a neutral buoyancy float), a scientific drifting bottle based on the messages in bottles that shipwrecked sailors hoped would reach inhabited shores, summoning assistance.

Swallow's invention Swallow designed his float to reach neutral buoyancy at a desired mid-water depth. The float emitted noises that could be tracked from a ship, allowing observation of the current velocity at the depth of the float. This ability to measure subsurface currents contributed to knowledge of the circulation patterns of the ocean. 1994 Henry Stommel Medal of the Woods Hole Oceanographic Institution