Jeremy Clarkson gets chased by the British Army in some of their latest and most deadly toys. Meanwhile, Richard Hammond and James May compare the new Porsche Panamera against a small envelope, a 39p stamp and the logistical might of the Royal Mail in a race from one end of the British Isles to the other. Plus, Olympic gold medal-winning sprinter Usain Bolt is the Star in a Reasonably Priced Car.