Two European nations purchase underwater drones amid Russia threat

Meanwhile, NATO countries have said they have deployed naval drones, in addition to frigates and patrol aircraft, as part of a mission to help protect critical infrastructure.

And Australia has said it will spend A$1.7 billion ($1.1 billion) on a fleet of Ghost Shark autonomous undersea vehicles, developed by its defence force and US startup Anduril Industries, for surveillance and strikes.

(Petra Wischgoll, Oliver Denzer and Cassell Bryan-Low; Editing by Alexander Smith)