The 308B grew directly from the Hesketh 308, which had been introduced in 1974 to replace the ageing March 731 chassis the team had been using since entering Formula One. Postlethwaite's design was loosely inspired by the March layout but incorporated original engineering thinking, most notably an unusual suspension system that used rubber springs rather than conventional coil springs. The idea came from a contact involved in designing rubber damping systems for buildings in earthquake zones. After early testing in 1974 proved unsuccessful, a non-creep rubber was developed by the Malaysian Rubber Producers Association and formed into springs by the Aeon Products company. Once suitable material was identified, the rubber springs were fitted from the 1975 Argentine Grand Prix onward.
Power came from the Ford-Cosworth DFV V8, the ubiquitous customer unit used by the majority of the grid's independent teams during the period. An ambition to develop a bespoke V12 engine was explored by Lord Hesketh but never realised.
For 1975, the 308 was updated to 308B specification with revised bodywork and repositioned oil radiators. The car proved immediately more competitive than its predecessor. Hunt challenged for victory in both Argentina and Brazil before the team's breakthrough came at the Dutch Grand Prix at Zandvoort, where he converted a strong position into an outright win. It was not only Hunt's first championship Grand Prix victory but also the only win the team would ever score.
Hunt supplemented the Dutch victory with a series of consistent points finishes across the season, giving Hesketh fourth place in the constructors' championship ahead of larger and better-resourced teams. Despite this competitive performance, the team's inability to attract a title sponsor — Lord Hesketh had been self-financing the operation — meant the money eventually ran out. At the end of 1975, Hesketh withdrew from Formula One as a constructor and Hunt departed for McLaren, where he would go on to win the 1976 World Championship.
The original 308 had debuted at the 1974 Race of Champions at Brands Hatch, where Hunt immediately took pole position. The first Grand Prix appearance followed two weeks later in South Africa: Hunt qualified thirteenth but drove to fifth place before being retired by a driveshaft failure. At the International Trophy at Silverstone — a non-championship race — Hunt delivered an impressive victory despite a slipping clutch and the gear-shift knob coming off in his hand during the race.
The 308 showed consistent pace but persistent mechanical fragility through 1974, with driveline failures costing Hunt strong results on multiple occasions. Accidents with Tom Pryce in the Netherlands and France also interrupted promising races.
With the team's closure, the 308 and 308B chassis were sold to privateer teams. Guy Edwards acquired one for 1976, attracting Penthouse magazine as a sponsor — a deal that generated notable publicity but no championship points. The car's competitive days were effectively over once the works team wound down.
The 308B's significance rests firmly on the 1975 season: it gave one of Britain's most colourful and unconventional Formula One operations its sole championship victory, and it launched James Hunt onto the podium stage he would occupy even more prominently in the years that followed.