This week an invisibility cloak tank was the star of an international arms and technology show in London. Invisibility and stealth is not a new idea, we've been trying to conceal weapons of war ever since they were first invented. In WWI dazzle paint was our best effort - crazed geometric patterns that confused the enemy's range finders. We've seen the bat-like stealth bomber, and now Sea Shepherd have their own stealth whale hunter tracking ship. Each has their challenges, not least that there is more than one way to detect a military vehicle. It's high time a simple Potter-style invisibility cloak was invented. It worked for Harry, surely it can work for the military.