'Submarine Sounding: Dover Patrol', 1917.
© Science Museum / Science & Society Picture Library
Watercolour and gouache painting on board by Norman Wilkinson, showing three airships hovering above the sea with a small ship in the background. Submarine sounding is a topographical method of ascertaining the depth of water. In the early 20th century water depth was measured by line sounding. A weight was lowered from the side of a ship or vesel by a sounding line and when it hit the ocean floor, the depth was indicated by the length of line extended. Wilkinson (1878-1971) studied art at the Portsmouth and Southsea Schools of Art, before going on to become a famous marine painter and a railway poster artist. He also made a significant contribution to the design of camouflage.