Since the US imposed sanctions on tanker company Dalian Tankers, owned by China's Cosco, about one third of Dalian's tanker vessels have turned off their Automatic Identification Systems (AIS), so the world cannot see where they are sailing, according to Reuters.

The US imposed a number of sanctions on Dalian Tankers Sept. 25, and since Sept. 30, 14 Cosco-owned tankers, six of which transport oil, have shut off their AIS systems, writes Reuters citing data from Refinitiv Eikon. Nine of the vessels are supertankers.