During World War II, a Great Western Railway passenger train was pursued by a German aircraft along the main line to Wales. Reaching speeds estimated at 90 mph (140 km/h), well above the wartime restrictions in place, the train successfully escaped into the tunnel and stopped beneath the river until the driver judged that the danger had passed. The train was struck by several bullets during the chase but there were no serious injuries.

Fun things I learnt whilst researching the Severn Tunnel.