In January 1943 the Yuma Test Branch of the Engineer Board of the Corps of Engineers began test operations on fixed and floating bridges at Imperial Dam, conducting tests in both sluiceways as well as above and below the dam, while bridge transportation equipment was tested in the desert and in the dunes west of Yuma. Troop units were ordered into the area to provide manpower for the tests and to train in river crossing operations, including the 87th, 88th, 553rd, and 555th Engr. Bns. (Heavy Ponton), the 527th Engr. Co. (Light Ponton), the 993rd Engr. Co. (Steel Treadway), and Co. E 33rd, Engr. Bn. (Armored), which assisted at various times. Under conditions of extreme urgency, these units aided tests that improved the capacities of light and heavy ponton bridges and led to the development of the steel treadway and M4 bridges, which were used successfully in the European and Pacific Theaters. The site continued in use after the war, and permanent structures were erected in what is now the headquarters area of the Yuma Proving Ground; the test branch closed in 1949 and reopened in 1951 as the Yuma Proving Ground.