March Engineering entered 1972 with high ambitions following a strong 1971 campaign. The intended centrepiece of the season was the 721X, a radical design conceived by Robin Herd. The 721X aimed to create a low moment of inertia by concentrating mass at the car's centre, and it used an Alfa Romeo transverse gearbox mounted between the Cosworth DFV engine and the rear axle. The concept was theoretically sound, but in practice the car never worked with the Goodyear tyres March was contracted to use. The front tyres were constantly overloaded, generating both oversteer and understeer in rapid alternation. Niki Lauda, one of the factory drivers that year, called it "a complete failure," "a stillbirth," and "a debacle." A basic customer version of the 721 — itself a modest evolution of the 1971 711 — had been supplied to Frank Williams Racing Cars and the Eifelland outfit, but the factory team had pinned its hopes on the 721X.
Recognising that the 721X was beyond rescue, March took the pragmatic decision to construct a replacement at maximum speed. The 721G was built in nine days, using a conventional Formula Two chassis from the March 722 as its foundation. Suspension and braking components were sourced from the customer 721, and the powertrain remained the Ford-Cosworth DFV V8. The approach was deliberately conservative: where the 721X had sought innovation at every point, the 721G relied on proven hardware assembled intelligently. The result was a car that could actually be driven at the limit.
The designation "G" distinguished it from the basic 721 and the ill-fated 721X. In the same season March had thus produced three distinct Formula One variants, an unusual feat that reflected both the constructor's agility and the urgency of the situation.
The 721G was raced by Ronnie Peterson and Niki Lauda for the March factory team during the second half of the 1972 season. Peterson proved the more effective driver with the new car. His best result came at the German Grand Prix at the Nürburgring, where he took third place — a podium that provided March with genuine evidence that the recovery had worked.
Lauda, competing in his first full Formula One season, failed to score points with either March chassis during the year. Despite his later fame as a two-time world champion, 1972 was a difficult initiation, compounded by the extended use of the flawed 721X before the 721G became available.
The 721G did not erase the damage done by the 721X, but it gave March a competitive baseline to work from. Its results, modest as they were, fed directly into the development of the 731 for the following season.
The 721G story is frequently cited as an example of pragmatic racing-team decision-making. Rather than persisting with a failed concept or withdrawing from competition, March stripped the problem down and rebuilt from a known-good starting point in under two weeks. The episode reinforced the value of proven Formula Two technology as a source of reliable Formula One hardware — a resource March would continue to draw upon in subsequent seasons. It also provided an early indicator of Ronnie Peterson's ability to extract results from imperfect machinery, a quality that would define much of his career.