For 1980, the Continental Mark VI replaced the Mark V after only three years of production. Originally slated to downsize the Mark series into the mid-size segment (adopting the chassis of the Ford Thunderbird), Ford instead chose an intermediate step for the Mark VI, adopting the full-size Panther platform, with the model line sharing much of its body with the 1980 Lincoln Continental. Alongside the traditional two-door coupe (sharing its 114-inch wheelbase used by Ford and Mercury), a first-time four-door sedan joined the Mark series (using the 117-inch wheelbase of Lincoln). While sharing much of its body with the all-new Continental/Town Car, many design elements of the successful Mark V made their return, including hidden headlamps, opera windows, and (non-functional) fender louvers; vertical taillamps were joined by a distinct spare-tire decklid. Coinciding with its smaller footprint, the Mark VI saw the standardization of fuel-injected V8 engines (a first for the American auto industry) and the first overdrive 4-speed automatic transmission; along with computer control for the engine itself, the instrument panel replaced analog instruments with digital displays (introducing a trip computer).