Russia’s Arctic coast is more than 15,000 miles long but the vast majority of it is off-limits. It’s part of a highly militarised "border security zone" where access is forbidden without special permission. In the past two decades, Russia has reopened and modernised more than 50 mothballed, Soviet-era military posts along its frozen frontier. It’s expanding its icebreaker fleet (which is already the world's biggest and most advanced) and, last October, Moscow test-fired a nuclear-powered cruise