A Bailey bridge is a type of portable, pre-fabricated bridge made of steel. It was designed during World War II by the British engineer Sir Donald Bailey. These bridges are known for their ease of assembly and disassembly, making them ideal for military and emergency use. Bailey bridges consist of modular components that can be transported easily and assembled quickly on-site. They can support heavy loads and span various distances, making them useful for both temporary and permanent applications in civil engineering and disaster relief efforts.