As an engineer, Casey prepared a voluminous report on flood control for the Pittsburgh District. He was involved with the design and construction of the Deadman Island Lock and Dam on the Ohio River, and was chief of the Engineering Division at the Passamaquoddy Tidal Power Project, a New Deal public works project. He went to the Philippines in 1937 to advise the government there on hydropower and flood control. In the early part of World War II, he became involved with the enormous wartime construction program. Perhaps his most notable and lasting achievement was his involvement with the design of The Pentagon, the largest office building in the world.