What was the first movie ever shown in CinemaScope to the public?

CinemaScope is an anamorphic lens series used, from 1953 to 1967, for shooting widescreen movies. Its creation in 1953 by Spyros P. Skouras, the president of 20th Century Fox, marked the beginning of the modern anamorphic format in both principal photography and movie projection.

Twentieth Century-Fox's pre-production of The Robe, originally committed to Technicolor Three-Strip origination, was halted so that the film could be changed to a CinemaScope production (using Eastmancolor, but processed by Technicolor). The film, The Robe, was the first movie ever shown to the public in CinemaScope.

During the making of How to Marry a Millionaire and Beneath the 12-Mile Reef, they also went into CinemaScope production. Millionaire finished production first, before The Robe. But, because of its importance and epic nature, The Robe was released first to the public.