Last week were digging around a prison, but this time Tony Robinson and co are taking us into the blue, as they aim to uncover the experimental origins of Britain's Submarine Service. Insert yellow submarine joke here. Tony and co will be off wreck diving and blowing things up underwater, with the aim of eventually finding out how these former death traps were transformed into deadly weapons that played a rather influential role in the First World War. We still haven't got a decent Beatles pun for this one...