Western observers have likely underestimated the number of Chinese nuclear submarines in development, but overestimated how many are operational, a new analysis suggests. In particular, only half of China’s nuclear-armed SSBNs appear to be in operation.

Photos of the Bohai Shipyard and the Longpo Naval Facility produced by Planet Labs suggest that “China does not yet have a credible sea-based deterrent,” said Catherine Dill of the James Martin Center for Nonproliferation Studies at the Middlebury Institute of International Studies at Monterey. Two of China’s four JIN (or 094)-class subs “appear to not be in operation and are undergoing maintenance or repairs at the Bohai shipyard, suggesting to us that credibility is still in question.”

That rebuts the Defense Department’s 2018 China Military Report and CSIS’s Chinapower group, which had stated that China had four operational 094s.