The term Caspian Sea Monster came about when U.S. satellites first spotted the large vehicle with stubby wings skimming over the waters of the Caspian Sea. Initially they thought it to be a prototype flying boat.
The Caspian Sea Monster (ekranoplan) was the world's largest and heaviest airplane like vehicle to be operated in ground effect.
No one in the world has yet managed to achieve the same smooth flight over water with such dimensions.