 You have to take out all the weight in the airship, basically, which is what the Germans did with their Zeppelins in World War I to bomb London. They took out all the weight so they could go to 15,000, 20,000 feet. But if you're going to carry anything at all, you've got to stay low. So by definition, they had to fly low. And 1,500 feet for a 777-foot-long airship. So think that the height above ground that R-101 was was twice its length.