Donald Bailey was a civil servant in the War Office who built model bridges as a hobby. In 1940, he sketched a bridge made of panels that fitted together. A few men could carry each panel, and the bridge needed no special tools or heavy equipment to assemble.
In 1947, Field Marshal Montgomery wrote that Bailey bridging had made “an immense contribution” to the outcome of the Second World War. His exact wording is given differently in different sources.