Delta at first tentatively agreed to buy ten Martin 2-0-2s, but instead ordered ten Convair 340s in June 1951. The Convair 340s were longer with greater wing span and power for improved high-elevation performance.
Delta's final ten Convair 340s were initially ordered by Chicago and Southern (C&S) Airlines. C&S merged with Delta on May 1, 1953.
Delta used the Convair 340 to promote its nighttime "Owl" discount coach services on its southern routes.
In 1956, Delta acquired the Convair 440, which was the same size as the Convair 340 but had improvements to reduce cabin noise level and increased operating weights. Delta retroactively modified all its Convair 340s to the -440 standard.