On the night of 16 February, 1926, during a snowstorm, Constable Williamson dived into the River Clyde to rescue a man who had attempted suicide. The river was flowing fast and the water was extremely cold. He had to swim about 40 yards to the middle of the river, still wearing his greatcoat. He reached the man and brought him successfully to safety.
Colleagues have said that it took him three hours to stop shivering after being in the cold water.
(London Gazette 1.1.1928)