The origin of these instruments dates back to WWII. Harold Rhodes, who was in the Army Air Corps, designed a portable piano that could be used towards therapeutic and pedagogical ends for wounded soldiers recovering in hospitals.
To produce sounds, hydraulic tubes from the wings of B17 bombers were cut to pitch and assembled into a 2.5 octave contraption.
From a 1945 copy of the official Air Force Journal: "The tinkling strains of many an old familiar song now are heard in AAF hospitals as the latest wrinkle in convalescent training comes into use. A poster series and an Air Forces Manual combine to invoke the possibilities of music as an immensely successful healer for both body and mind."
Years later, Harold Rhodes partnered with Leo Fender to manufacture the modern Fender Rhodes which became simply the Rhodes in the 1970s.
The one we use is from 1972. It was completely overhauled by one of the world's top Rhodes techs, David Ell out of Washington state.