The last of China’s nuclear-powered attack submarines was sunk a few months ago, a senior US defense official said today, a development that potentially embarrasses Beijing as it seeks to expand its military capabilities.

China already has the world’s largest warship, with more than 370 ships, and has begun production of a new generation of nuclear-capable submarines.

The US official, who asked not to be named, said the new nuclear-powered attack submarine sank alongside a pier sometime between May and June. It is not clear what led to its sinking, nor whether it was loaded with nuclear fuel.

“Aside from the obvious questions about (crew) training and materiel quality, the incident raises deeper concerns about the level of PLA accountability and oversight of China’s defense industry, which has long been plagued by corruption,” added the same source.

“It’s no surprise that the PLA attempted to cover up” the sinking, he said.

China’s embassy in Washington did not respond to a request for comment. The news was first reported by the Wall Street Journal.

Satellite images from Planet Labs taken in June show cranes at the Wuchang shipyard where the submarine is supposed to be docked.

In 2022, China had six nuclear-powered ballistic missile submarines, six nuclear-powered attack submarines and 48 diesel-powered attack submarines, according to a Pentagon report on Beijing’s military capabilities. The submarine force is expected to grow to 65 by 2025 and 80 by 2035, the Ministry of Defense estimates