After the war he became successful in business ventures in several different fields including insurance, steel, railroads, utilities and banking.

The plant built one craft a day and floated them more than 1,000 miles down the Missouri and Mississippi Rivers to New Orleans, Louisiana, prompting their "Prairie Ships" nickname.

Darby's plant at the mouth of Kansas River could hold 8 135í LCTs and 16 Landing Craft Mechanizeds (LCMs) in various stages of construction.

On December 2, 1949, he was appointed to fill a United States Senate seat to replace Clyde M. Reed (who had died on November 8) by Governor Frank Carlson, despite the fact that his only prior government experience was four years on the state highway commission.

As a senator, Darby was a friend of General Dwight D. Eisenhower, a fellow Kansan.