NATO has warned all member states that the nuclear-capable submarine has deployed. The Belgorod has disappeared from its home base in the Arctic Circle and may be on its way to the Kara Sea to test the Poseidon nuke, a NATO warning note leaked to Italian media over the weekend has suggested. According to a report by The Daily Mail, Poseidon is a drone that is said to be capable of traveling huge distances underwater before detonating with enough force to trigger a 1,600ft nuclear tsunami designed to drown and irradiate coastal cities.

NATO has since sent a warning to all allies that the sub has gone missing, but said it is still thought to be operating in the Arctic. It is unclear exactly when the warning was sent, but it was first reported by the Italian newspaper La Repubblica on Sunday.

The Belgorod submarine has been in operation since July. It was originally suspected that this sub played a role in the destruction of the Nord Stream pipelines. However, its absence would have been immediately noted and it would have had to travel over 3,000 miles from the Arctic to damage the pipelines in the Baltic Sea.