Ex-USAF pilot John M. Conroy realized that these aircraft could be modified to transport the large but relatively light rocket components.

[1] Conroy presented his plans for an extensively modified Stratocruiser to NASA, where an official commented that the bloated aircraft resembled a pregnant guppy.

The entire rear section, including tail surfaces, was detachable to allow cargo to be loaded directly into the fuselage.

[3] When Van Nuys traffic control realized that Conroy intended to take off, they notified police and fire departments to be on alert.

The Guppy delivered the S-IV Saturn I rocket stage three weeks faster than a barge,[4] for a cost of $16.00 (equivalent to $157.18 today) per mile (1.6 km).

Among its early duties was transporting the first and second stages of the Gemini program's Titan II from the Martin Co. in Baltimore, Maryland, to Cape Canaveral.