Bailey bridge

A Bailey bridge is a factory made truss bridge. It was made in small sections that could be easily moved and put together on site. It was developed by the British during World War II for military use. 
A Bailey bridge did not need special tools or heavy equipment to put into place. The wood and steel bridge parts were small and light enough to be carried in trucks and lifted into place by hand. The bridges were strong enough to carry tanks. Bailey bridges continue to be used in building projects and to provide temporary crossings for people and vehicles. 
It was designed by a British engineer, Donald Bailey. The British army tested different bridge designs in 1941–1942, including a suspension bridge and a stepped arch bridge. The flat truss bridge was the most successful. An early test model of the Bailey flat truss bridge is still in place over Mother Siller's Channel in Dorset. The Bailey bridge was first used by the army in Tobruk in 1942. The US Army built many of the bridges for use after the D-Day landings in France.
Parts of the bridge.
The basic Bailey bridge is made up of three main parts, the "floor", the "stringers" and the side "panels". The floor of the bridge is made up of a number of that run across the bridge. Across the bottom of these, forming a square, are . The bridge's strength is provided by the panels on the sides. The panels are , , cross-braced rectangles. Each weighs , and can be lifted by six men.
The transoms rest on the lower part of the panels, and are held together by clamps. The stringers are placed on top of the completed structural frame, and large pieces of wood are placed on top of the stringers to provide a roadbed. Ribands bolt the planking to the stringers. Later in the war, the wood was covered by steel plates, to protect it from the damage caused by tank tracks.
Each unit built in this way is a single section of bridge, with a roadbed. After one section is complete it is pushed forward over rollers on the bridgehead, and another section built behind it. The two are then connected together with pins pounded into holes in the corners of the panels.
Modern Bailey bridges.
Bailey bridges are in regular use throughout the world. Some examples include:
Other uses.
The Skylark launch tower at Woomera was built up of Bailey bridge parts.