Vietnam’s military is steeling itself for conflict with China as it accelerates a decade-long modernisation drive, Hanoi’s biggest arms buildup since the height of the Vietnam War. The ruling Communist Party’s goal is to deter its giant northern neighbour as tensions rise over the disputed South China Sea, and if that fails, to be able to defend itself on all fronts, senior officers and people close to them told Reuters.

Vietnam’s strategy has moved beyond contingency planning. Key units have been placed on “high combat readiness” - an alert posture to fend off a sudden attack - including its elite Division 308, which guards the mountainous north.

The two countries fought a bloody border war in 1979. The likely flashpoint this time is in the South China Sea, where they have rival claims in the Spratly and Paracel archipelagos. “We don’t want to have a conflict with China and we must put faith in our policy of diplomacy,” one senior Vietnamese government official, who spoke on condition of anonymity, told Reuters. “But we know we must be ready for the worst.”

Most significantly, Hanoi is creating a naval deterrent largely from scratch with the purchase of six advanced Kilo-class submarines from Russia. In recent months, the first of those submarines have started patrolling the South China Sea, Vietnamese and foreign military officials said, the first confirmation the vessels have been in the strategic waterway.