The diminutive Cooper T39 Bobtail had an outsized impact on mid-century motor racing, incorporating the latest in mid-engine chassis design and aerodynamics.

Its truncated rear end—the “bobtail”— borrowed from German engineer and designer Wunibald Kamm’s previous work, was a novel and effective feature that improved airflow.

Powered by lightweight Coventry Climax inline four-cylinder engines, the T39 Bobtail was the Cooper Car Co.’s first major foray into mid-engine chassis design and paved the way toward the company’s eventual success in Formula 1.

Raced by the likes of Sir Jack Brabham, Graham Hill, Sir Stirling Moss, Roy Salvadori, and Jim Russell, its immediate success on circuits helped seed the mid-engine layout that is used in most purpose-built racecars today.

Cooper Car produced 40 to 50 examples of the T39 Bobtail from 1955 through 1957.

This beautifully restored example is believed to be one of only 13 surviving—a Mark II, which the company updated with a larger cockpit...