Nato's new technology for tracking Russian submarines

Nato has been carrying out its largest ever anti-submarines warfare exercise in the North Sea.

It is seen as a response to increasing activity by Russian subs - there have been recent reports of them operating off the coast of Scotland as well as Sweden and Finland.

Defence Correspondent Jonathan Beale went on board the Nato research ship, RV Alliance, to see them testing the latest unmanned technology to hunt for submarines.