Work began on the main facility area on 20 October 1943. Although generally flat, some of soil and rock had to be excavated from areas up to high, and six major areas had to be filled in, to a maximum depth of . Normally buildings containing complicated heavy machinery would rest on concrete columns down to the bedrock, but this would have required thousands of columns of different length. To save time soil compaction was used instead. Layers were laid down and compacted with sheepsfoot rollers in the areas that had to be filled in, and the footings were laid over compacted soil in the low-lying areas and the undisturbed soil in the areas that had been excavated. Activities overlapped, so concrete pouring began while grading was still going on. Cranes started lifting the steel frames into place on 19 January 1944.