In times of war the crossing of physical barriers, such as rivers, caused the greatest delays to advancing armies. At the same time the physical barrier was usually manned by defence forces further restricting movement. The use of bridges were thus critical to the success of overcoming these obstacles and furthermore it was essential that these bridges were erected in the shortest possible time.
The ideal solution is that the method of bridge building is kept as simple as possible whether crossing a ravine or a river. In addition, the repetition of parts or modular units simply assembled and the weight minimised to facilitate the transport of parts was critical. It should be possible for men to manhandle parts, without cranes etc., and require the minimum of supervision or skill. At the same time these bridges had to be capable of carrying wagon trains of armaments or, as in World War II, the weight of tanks.
The Bailey Bridge, named after Sir Donald Bailey, was one such bridge developed for use in the second World War. The success of this bridge was due to its modular design and that it could be assembled with the minimum of heavy equipment. The bridge could be assembled on the bank and then pushed out over the river. A temporary nose piece, angled upwards, assisted the landing on the far river bank and compensated for any deflections or level differences.
The Bailey Bridge was also designed to be used with pontoons as temporary supports crossing rivers and modular piers could be assembled to form vertical towers as intermediate supports when crossing valleys.
The appropriate load carrying capacity of a Bailey Bridge was catered for by combining the modular units into double or treble width and similar in height, thus making it a most versatile piece of equipment. The modular panels are 3.0m long and 1.5m high and weigh 260kgs which can be lifted by six people. The width of the bridge is normally 3.7m. The panels are connected together using pins and movement out over the space to be spanned is assisted by rollers and trucks. Timber or steel plates are used for decking.
The longest Bailey Bridge was commissioned in October 1975 over the Dervent River at Hobart, Australia. It measured 788m and functioned for two years while a new permanent bridge was constructed.
This form of bridge building has also developed with the evolution of new higher strength materials. In the modern type of bridge, alloy metals now form the panels making them lighter. A similar type of bridge, but manufactured by a competitor, is the Maley Bridge but it has not become as well known as the original invention.