Hendricks Army Airfield had operated as a training base for B-17 bomber pilots between 1941 and 1946. After the war, Russian-American aeronautical engineer Alec Ulmann identified the site's network of concrete runways, taxiways, and perimeter roads as suitable for a sports car endurance race modelled on the 24 Hours of Le Mans. Ulmann wanted to bring a similar endurance challenge to North America, and Sebring's flat, sprawling airport geography provided the necessary space.
The site held its first race on New Year's Eve 1950, a six-hour event called the Sam Collier Memorial Grand Prix, won by Frits Koster and Ralph Deshon driving a Crosley Hot Shot. The event attracted thirty cars and proved the concept viable. Two subsequent events followed before the circuit was formalised as the venue for the first full 12 Hours of Sebring on March 15, 1952.
The 1952 circuit retained the defining quality of the entire Sebring project: its surface. World War II-era concrete runway sections, laid in large panels with prominent expansion joints and seams between them, formed the backbone of the course. Transitions between concrete slabs produced pronounced bumps and vibration. Unlike European road circuits of the era, Sebring offered almost no elevation change, Florida's flat interior providing little topographic variety around the layout.
The course measured approximately 5.2 miles (8.369 km), a figure that remained standard at Sebring for much of the track's early history. It incorporated long straight sections along the former runway alignment — giving cars room to reach high speeds — connected by a series of slower bends and corners using the airfield's perimeter and service roads. The geography meant drivers needed a thorough knowledge of the circuit to navigate it reliably, particularly at night: early competitors and commentators noted that the poor marking of the runway sections made it surprisingly easy to become disoriented and temporarily lose the track entirely, especially in darkness.
The 12 Hours of Sebring in 1952 established the event within the international sporting calendar. It grew into a major fixture of the World Sportscar Championship, attracting factory entries from European manufacturers alongside American teams. The first 12 Hours was held on March 15, 1952, and quickly became the target race for teams building toward the 24 Hours of Le Mans, offering comparable mechanical stress and a similar requirement for endurance-focused preparation in a very different environment.
Sebring's airport heritage gave the circuit properties unlike any other major endurance venue. The concrete runway surface, deliberately preserved in subsequent years as a defining characteristic, imposed extreme mechanical loads on cars through vibration and bumping, making the 12 Hours notoriously hard on brakes, suspension, and driver endurance. Mario Andretti, who won at Sebring three times, described one of the hardest elements of the original track as "finding the track to begin with," a reference to the disorienting expanse of barely differentiated concrete surfaces.
The 1952 layout set the template for Sebring's core identity: long straights for flat-out running, technical slower sections on the perimeter roads, and a surface that punished machinery more severely than almost anywhere else in international racing. Subsequent layout changes — a 1966 tragedy prompted widening and the replacement of the Webster Turn with the Green Park Chicane in 1967, followed by revisions in 1983, 1987, and 1991 — progressively modernised the course. However, the original 1952 vision of racing across repurposed military runways remained the philosophical and physical foundation of the Sebring International Raceway that continues to host the 12 Hours today.
The 1952 event is recognised as the starting point of American sports car endurance racing as an internationally credible discipline, and the airport circuit configuration established in that year shaped the nature of Sebring more lastingly than any subsequent revision.