STEEL TREADWAY BRIDGE from Simbach, Germany, to Braunau, Austria, replaces the one destroyed by retreating Germans, May 1945. The United States Army in World War II-The Technical Services- Engineers- Volume 1
One of the things that had the Engineers pulling their hair out in the war was the ever increasing weights of military vehicles. In 1938, a 12 ton capacity was considered sufficient for bridging equipment at the division and corps level. By 1943, the Engineers faced the need for bridges to bear weights of 35 tons or more.
Take a look at the treadway bridge. How would you increase its capacity? The simple answer is to make each float bigger, and thus more buoyant. That’s what the Engineers did. That worked from the capacity point of view, but imposed two penalties. First, the larger floats were more difficult to transport to the crossing site, requiring more and larger trucks in the divisional and corps trains.
Secondly, and from the Corps of Engineers point of view, worse, every required increase in capacity meant that previous equipment was obsolete, and production had to be shifted to new equipment. The iron law of mass mobilization calls for freezing a design as early as possible. Having to constantly switch designs slowed the accumulation of stockpiles of bridging equipment, and meant that bridging companies rarely had sufficient stocks on hand for realistic training before deploying overseas.
Further, in the early years of the war, there were a plethora of bridge types available. Each needed its own special skills for emplacement. While the total number of bridge designs authorized didn’t really decline, by the end of the war, as a practical matter, most bridging was done with either the steel treadway bridge shown, or semi-fixed Bailey bridges adopted from Great Britain.