AMA racing

Hennen was born in Phoenix, Arizona and grew up in the San Francisco Bay Area, where he first became interested in racing motorcycles at the age of 15.^[2][4] After spending four years developing his riding skills in regional races, he entered his first professional event as a novice at the end of the 1971 season.^[2]

Although his results in dirt track racing were promising, Hennen chose to focus his attention on road racing.^[2] In 1973 he competed in 250cc Junior road racing events riding a borrowed Suzuki built by his brothers, Chip and David Hennen.^[2] He began to work for Suzuki factory road racer Ron Grant by helping him prepare motorcycles out of Grant's home garage.^[4]

The first major victory of Hennen's motorcycle racing career came in 1974 at the Daytona International Speedway when he set the fastest qualifying time and won the junior event on a Ron Grant-sponsored Yamaha.^[2] Hennen went on to win the Junior races at the Loudon Classic, Laguna Seca, and Talladega to become the 1974 AMA Junior road racing champion.^[5]

Hennen gained his first international exposure in 1974 when Grant took him to compete in the New Zealand Marlboro Series run over the Christmas/New Year period where, he made a positive impression by winning the series three years in succession from 1975 to 1977.^[6] The Suzuki importer for New Zealand was former Grand Prix racer and 1954 Isle of Man Junior TT winner, Rod Coleman, who along with Grant, would be instrumental in helping further Hennen's professional motorcycle racing career.^[4]

Hennen's racing success earned him a contract to race for U.S. Suzuki's factory road race team for the 1975 season, alongside teammate and multi-time AMA National Champion Gary Nixon.^[2] He was a member of the American team competing in the 1975 Transatlantic Trophy match races.^[2] The Transatlantic Trophy match races pitted the best British riders against the top American road racers on 750cc motorcycles in a six-race series during Easter weekend in England. That year, the United States won over Great Britain for the first time.^[2]

Hennen showed promise in the AMA national championship by claiming the pole position at the Ontario Motor Speedway, but his motorcycle experienced mechanical issues and his best result of the season was a fifth place at Laguna Seca.^[2] The 1973 oil crisis severely impacted all forms of motorsports in the United States and Suzuki made the decision to withdraw their team from the AMA national championship at the end of the 1975 season, leaving Hennen without a job until Rod Coleman offered him a Suzuki TR750 race bike which he had salvaged after learning that the factory planned to discard it.^[4]

Hennen rode the ex-factory motorcycle, built from discarded spare parts, to a dominating win at the 1976 New Zealand Marlboro Series, then scored an impressive third place at the 1976 Daytona 200 behind Johnny Cecotto and Gary Nixon, now riding for the Kawasaki factory racing team.^[4][7] At the time, the Daytona 200 was considered one of the most prestigious motorcycle races in the world, attracting world champions such as Giacomo Agostini and Barry Sheene.^[8] Hennen also rode a Yamaha TZ 250 in the Daytona 250cc Lightweight race, finishing second to Kenny Roberts after a race-long duel.^[7] Hennen was magnanimous after the 250cc race declaring that, "Roberts was poetry on two wheels".^[7]

World Championships

In 1976, Suzuki began to sell production versions of Barry Sheene's World Championship-winning Suzuki RG 500 to the public. Inspired by Hennen's success, Coleman purchased an RG 500 for Hennen to compete in the 1976 500cc Grand Prix World Championship as a privateer.^[4] He also competed in the fledgling Formula 750 series on the same ex-factory TR750 he rode at Daytona that year.^[4] The 500cc World Championships were the highest level of professional motorcycle road racing during that era. Hennen competed on a shoestring budget, driving to races across Europe in a small van with his brother Chip serving as his team manager as well as his mechanic.

When they arrived in France for the season-opening 1976 French Grand Prix, some observers laughed at the raw, inexperienced team.^[9] Although, they received valuable spare parts and assistance from Merv Wright, the manager of Suzuki's British-based factory Grand Prix team, this displeased Suzuki's number one rider, Barry Sheene, who recognized the threat that Hennen posed to his position at the top of the team's hierarchy.^[4]

After a slow start to the 1976 season, Hennen finished runner-up in the Dutch TT at Assen, behind Sheene and ahead of multi-time World Champion Giacomo Agostini.^[1] However, Sheene was at the peak of his career and won five of the first seven Grand Prix races to claim the World Championship at the Swedish Grand Prix, then chose to sit out the final three rounds as he disliked riding the dangerous circuits remaining on the schedule.

Sheene's absence then allowed Hennen to score an upset victory over Teuvo Länsivuori and Agostini at the 1976 500cc Finnish Grand Prix to become the first American competitor to win a 500 cc World Championship Grand Prix race.^[4][10] His upset victory was so unexpected that the Finnish race organizer did not have a copy of the American national anthem to play during the awards ceremony.^[10] Hennen said in a 1977 interview that local rider Länsivuori helped him win the race by allowing Hennen follow him during practice to learn the 3.747 miles (6.030 km) long street circuit, and see where the track's uneven surface held hidden bumps even on its straight sections.^[2] The Imatra Circuit, home of the Finnish Grand Prix, was notoriously dangerous featuring curbs, manhole covers, street signs and light poles along with a railroad crossing.^[11]

The final race of the season was the German Grand Prix held at the daunting, 14.2 miles (22.9 km) long Nürburgring racetrack, considered too dangerous for the Formula One championship. Despite racing on the circuit for the first time, Hennen finished the race in an impressive third place behind Agostini and future World Champion Marco Lucchinelli.^[1] Competing as a privateer rider against factory-sponsored teams, he scored two podium results along with his maiden Grand Prix victory to finish third overall in the 500cc World Championship standings, only 2 points behind runner-up Länsivuori and fellow Suzuki factory-sponsored rider Sheene.^[1]

Having established himself as one of the top three 500cc riders in 1976 earned Hennen a position on the Heron-Suzuki factory racing team for the 1977 season, with newly crowned 500cc World Champion Sheene as his teammate. Sheene continued to treat Hennen with animosity by commandeering the best equipment for himself.^[4][12] Hennen was forced to skip the 1977 Daytona 200 because Suzuki had not finished developing their 750cc race bike but, he was the top points scorer at the 1977 Transatlantic Match races.^[13] At the mid-point of the season, Hennen traveled to the Isle of Man to compete in his first Senior TT race however, he experienced mechanical problems and did not finish the race.^[14]

Despite Sheene's continuing animosity, Hennen scored four podium positions including beating Sheene at his home Grand Prix at the Silverstone Circuit.^[1] The 1977 British Grand Prix marked the beginning of a new era, as it was the first time the event was held on the British mainland after the Isle of Man TT had represented the United Kingdom on the FIM Grand Prix calendar for the previous 28 years since the championship's inception in 1949.^[15] Once the most prestigious race of the year, the Isle of Man TT had been increasingly boycotted by the top riders, and finally succumbed to pressure for increased safety in racing events.^[15]

Sheene had taken the lead of the Silverstone race when a mechanical issue forced his retirement.^[16] Steve Parrish then led the race ahead of John Williams with Hennen in third place as they began the final lap, when Parrish crashed out of the lead, and then Williams did the same three corners later, handing Hennen his second career Grand Prix victory.^[16] He ended the season once again ranked third in the world championship behind Sheene and Yamaha rider, Steve Baker.^[1] He finished the year by performing a hat-trick with a victory at the prestigious Mallory Park Race of the Year as well as the Motor Cycle News-Brut 33 Superbike Championship round and the 500cc final.^[17][18]

Hennen began the 1978 season by dominating the 1978 Transatlantic Match races, winning three races as well as two second places and one third place, becoming the top scorer in the prestigious event.^[19] His battle with his Suzuki teammate continued, when Sheene accused him of performing a dangerous pass.^[19] Seeking a psychological advantage over his rival, Sheene publicly disparaged his American teammate, telling journalists, “If you pay peanuts, you get a monkey.” however, his tactics had no effect on the quiet, easy-going Hennen.^[12]

After Yamaha withdrew from the AMA Grand National Championship, Roberts joined Hennen in the 500cc world championship, where the American duo posed the strongest threat to Sheene's two-year reign at the beginning of the 1978 season. Hennen scored a second place behind Sheene at the season-opening Venezuelan Grand Prix before claiming the world championship points lead by winning the third Grand Prix victory of his career at the Spanish Grand Prix held at Jarama.^[1][20] Roberts then won the next three rounds with Hennen posting two second places, as the two Americans were separated by only a single point atop the world championship standings when Hennen suffered career-ending injuries while competing in the 1978 Isle of Man TT race.^[2]

By 1978, most of the top Grand Prix riders, including Sheene refused to compete in the Isle of Man TT races due to the dangers of racing on a street circuit however, the British-based Suzuki factory team wanted one of its top riders entered into the event so, Hennen was called upon to race.^[4] Tom Herron was leading the race with Hennen aggressively pursuing him in second place. Only minutes after recording the first ever sub-20 minute lap on a 500 cc Suzuki, Hennen crashed at Bishopscourt on the last lap of the race.^{[21][22][23][24]} There was a suggestion at the time that he had struck a bird although this is now considered an unfounded rumor.^[4] Hennen's injuries proved to be too severe and he was never able to compete again.^[2][4] Roberts would go on to win the 1978 championship to become America's first 500cc Grand Prix World Champion.^[2]