European Union waters will be severely constrained following Brexit. The vessels of Baltic and Benelux countries will have to transit United Kingdom waters to reach the high seas; or go the long way via the waters of the Faroe Islands, Norway and Iceland. In peacetime, and with compliance of the rules of innocent passage, this should not be a problem. In a war scenario the situation will be very different. Assuming that NATO is not undermined by the new EU army and defence union, it can be anticipated that the only credible threat to the UK mainland would come from the air-force and navy of the Russian Federation. Because of treaty obligations the UK would be obliged to respond to aggression anywhere against a NATO partner. In reality the priority for the UK would be to stop the Russian Navy reaching the high seas of the North Atlantic through the Greenland Iceland United Kingdom (GIUK) gap, and the Russian Airforce coming down the coast of Norway in to the North Sea or via the west coast of Ireland. The next priority would be to deter or oppose an anticipated invasion by the Russian Army across its land border with Norway by the deployment of airborne and amphibious forces. Given the current state of the UK armed forces this is a big ask, especially for the Royal Navy that is being stretched like an elastic band and in danger of snapping.