John Worsley joined the Royal Navy in 1939. His depictions of life on board ship were soon acquired by the War Artists Advisory Committee (WAAC), and he was quickly made an official war artist. In 1943, he was captured in the Mediterranean and spent the rest of the war in a naval officer's prison camp, Marlag ‘O’ at Westertimke, near Bremen in north Germany.
1944 was a turning point during the Second World War, when bomber raids over Germany had become a regular occurrence. In Marlag ‘O’, the inmates congregated outdoors to watch the vapour trails left by American Flying-Fortress bombers. These were ominous markers: they made the aircraft conspicuous targets and announced an imminent attack. For the PoWs, they brought hope. The watercolour suggests a sense of space and freedom, which contrasts with the confines of the camp from which the sky is viewed.