Chinjao was the 12th commander of the Happo Navy, but after Vice Admiral Garp caused his famed drill-shaped head to cave in, he lost his legendary strength, and access to the vast fortune buried inside the Jewel Ice Sheet. Losing everything and left with a broken heart, he gave up on piracy, and retired.
His position as the commander succeeded by his grandson, Sai, while his other grandson, Boo, became the lieutenant.
While Chinjao was fighting Luffy at the Corrida Coliseum, Luffy dealt a strong blow on his head recovering his drill-shaped head once again.
After the fight, while Chinjao was struggling to thank Luffy for bringing his head back to its original shape. Chinjao said that he will put his grandson's Happo Navy Army under Luffy's wing as a token of gratitude.
After Sai defeated Lao G and bent Chinjao's restored drill-shaped head with a kick, Chinjao proudly stated that his grandson has inherited the Hasshoken's secret technique, and is now truly worthy of being the Happo Navy's captain.
The Happo Navy consists of a large fleet of ships,, with the position of leader being passed down for 13 generations. The army was strong enough to survive an encounter with Vice Admiral Garp, and has amassed a great cove of treasure.
The Happo Army's signature combat technique is the Hasshoken, which allows the user to emit vibrations in a physical strike, breaking through shields and defenses and inflicting heavy damage. The vibrations can be imbued in virtually any melee attacks, such as fists, elbows, and kicks. It is similar to one of the applications of the Gura Gura no Mi.