 Complete the following phrase:  The two Hindenburg-class airships were hydrogen-filled, passenger-carrying rigid airships built in Germany in the 1930s and named in honor of Paul von Hindenburg. They were the last such aircraft to be constructed, and in terms of their length, height, and volume, the largest aircraft ever built. During the 1930s, airships like the Hindenburg class were widely considered the future of air travel, and the lead ship of the class, LZ 129 Hindenburg, established a regular transatlantic service. The destruction of this ship in a 