The first Cadillac Eldorado Brougham was a one-off show car which made its public debut at the 1955 GM Motorama. This car was the direct predecessor of the ultra expensive, limited production Eldorado Broughams, which was built in 1957 and 1958. A pillarless four-door hardtop with center opening doors, and swiveling driver seat, the experimental 1955 Cadillac Eldorado Brougham incorporated some of the basic styling elements from the 1954 Park Avenue concept vehicle, including large front wheel cutouts, a notched rear roofline and forward swept tail fins.

The Brougham concept had quad headlight units with an Autronic Eye, brushed stainless steel roof, air suspension and was painted chameleon green. Exhaust gases were channeled thru portin the rear bumper.

Some of these car styling features were later seen on the production 1957 Cadillacs.

Note: Both front seats of the prototype Eldorado Brougham of 1955 were of the swivel type. This is borne out by a period photo showing the control knob located on the side of the passenger seat.

source: history.gmheritagecenter.com