Merchant seamen receiving instruction in the art of anti-aircraft gunnery through the services of a mobile DEMS (Defensively Equipped Merchant Ships) course. In this image, the seamen are being trained to track and ‘lead’ an approaching enemy aircraft through the gun sight of a close range anti-aircraft weapon. The 'target' is a small model aircraft suspended from the side of the converted double-decker bus. The port in which this scene took place has yet to be identified.