His formal education was interrupted by World War II, during which he served in the Navy in the Aleutians as a chaplain's assistant.
At first, this role consisted of transferring 78 rpm recordings of Enrico Caruso and Artur Schnabel to tape, including removing surface noise preparatory to LP reissue.
He also assisted at sessions for Kirsten Flagstad, Vladimir Horowitz, William Kapell, Wanda Landowska, and Zinka Milanov.
In 1954, he worked with Leopold Stokowski and the NBC Symphony Orchestra on the experimental stereophonic recordings of ballet suites from Gian Carlo Menotti's Sebastian and Prokofiev's Romeo and Juliet, which were not commercially released in stereo until 1978.
With Westminster struggling (the company filed for bankruptcy in December 1959), he switched to recording pop singers including Eddie Fisher.
Their first major project was a 12-LP set for Reader's Digest Recordings: A Festival of Light Classical Music, issued in both monaural and stereophonic versions.
In 1961, he produced the Reader's Digest set of Beethoven symphonies with the Royal Philharmonic Orchestra conducted by René Leibowitz.
One particularly successful set Gerhardt conducted with the National Philharmonic Orchestra included the 14 LPs of the Classic Film Scores series for RCA, issued 1972–1978.
A compilation album distributed promotionally in 1989 titled "The Home Video Album" featured the Studio themes and some duplication of "The Spectacular World of Classic Film Scores" but also includes a suite from Dimitri Tiomkin's "The Thing from Another World as well as an amusing version of the 20th Century Fox Title, as orchestrated and performed by John Morris for Mel Brooks' send-up of Alfred Hitchcock, "High Anxiety".
In 1979, Gerhardt conducted the National Philharmonic Orchestra in Korngold's score for the Warner Brothers' 1942 film version of Kings Row, also produced by the composer's son George.
In 1989 Varèse Sarabande released an album "Music from The Prince and the Pauper" and other films with the National Philharmonic Orchestra (VSD 5207.