 Constructed mostly of steel, it was an American version of the German Wasserfall anti-aircraft missile; the Wasserfall was about 1/2 the size of the German A-4 (V-2).Hermes A-1 had one major difference from the Wasserfall.The Peenemünde Nitric Acid/Visol (vinyl isobutyl ether) fueled P IX engine was replaced by a General Electric pressure fed 13,500 lb.