a four-door Southampton hardtop sedan was added to the range. 10,268 were produced. With a wheelbase of , longer than the previous year's by , they had the longest wheelbase ever for an Imperial. This also contributed to an increase in their overall length to , making them the longest non-limousine post-WWII American cars until the advent of the Imperials of the "Fuselage Look" era in the 1970s. 1956 was the year that Chrysler introduced the push button PowerFlite automatic transmission becoming available mid-year with the control pod installed to the left of the driver; Packard also introduced a similar system called the Touchbutton Ultramatic in the Imperial's competitor, the Packard Caribbean and the Patrician. For 1957, Mercury introduced its version called "Keyboard Control" for the Merc-O-Matic, which also included a pushbutton to place the transmission in neutral so the engine could be started and a push/pull control to set the parking brake and lock the transmission in gear. The Mercury and Chrysler versions were operated mechanically while the Packard and the controversial and short lived Edsel Teletouch version used electric solenoids to change gears. On April 28, 1955, Chrysler and Philco announced the development and production of the world's first all-transistor car radio, the Mopar model 914HR. It was developed and produced by Chrysler and Philco and was a $150.00 "option" on the 1956 Imperial car models ($ in dollars ). Philco manufactured the Mopar 914HR starting in the fall of 1955 at its Sandusky Ohio plant, for Chrysler. Second generation (1957–1966) For the 1957 model year, the Imperial received its own platform, setting it apart from any other division of Chrysler and shared the all-new "Forward Look" appearance, showing many styling features introduced with the concept car Chrysler Norseman. Overall, this made the front end loosely resemble the smaller 1957 Plymouth Savoy. This would last through the 1966 model year. Imperials during this period were substantially wider, both inside and out, than other Mopars, with front and rear shoulder room equal to and respectively. The front seat shoulder room measurement remains an unsurpassed record for Imperial and would remain the record for any car until the 1971–1976 GM full-size models. Exterior width reached a maximum of for 1961–1963, which remains the record for the widest non-limousine American car. After Lincoln downsized for 1961, this generation of Imperial had no real competitor for the title of largest car for