The Silhouette, "designed" by Harry Bradley for Mattel, was based on the 1963 show car built by Bill Cushenbery in 1962. It's most prominent feature was the bubble top, a popular item for show cars at the time.
Cushenbery's original was purchased by the Ford Motor Company in 1963 and included in their Ford Custom Car Caravan road show. It was apparently stolen in recent years and gone missing.
AMT made a popular scale plastic model kit and added a similarly styled custom trailer.
There is a YouTube clip from the 1967 television special, The Wonderful World Of Wheels. The show yielded another kit release.
In 1964 Cushenbery started to work on the Corvair-powered Silhouette II but did not complete it.
In the '90s Mattel created their own Silhouette II a less radical departure from the original. For a drive down memory line try WONDERFUL WORLD OF WHEELS DVD host Lloyd Bridges.