China’s newest nuclear-powered submarine sank pierside in the spring and the Chinese Navy tried to conceal the loss, according to two US defense officials.

China’s newest nuclear attack submarine has sunk in a shipyard accident, in a setback to the country’s attempts to overtake the United States in a naval arms race, according to US officials.

The pierside accident came as Beijing, which hasn’t acknowledged the episode, attempts to expand its navy and project its military power.