George Nissen invented the modern trampoline, which made trampolining a worldwide sport and recreation. He was born in Blairstown, Iowa, in 1914 and began training in gymnastics as a child, tumbling on his junior high school tumbling team and a local YMCA team when he was in high school. In 1930, at the age of 16, he attended a circus performance where he saw acrobats falling onto safety nets, finishing their descents with somersaults. Nissen considered the opportunities for gymnasts like him using a similar apparatus. Over the next few years, he created a few prototypes using materials he could find, including iron from the local scrapyard and his own bed. In 1934, Nissen and his coach, Larry Griswold, built the prototype trampoline from angle iron with a canvas bed and rubber springs. Nissen used it to help with his training and to entertain children at a summer camp. He received the patent for his "Tumbling Device" on March 6, 1945, for which he later registered the trademark "trampoline," inspired by "el trampolin," Spanish for "diving board". Some of his first buyers were the United States military and NASA, who used it as a tool to train pilots and astronauts to quickly adapt to changing orientations.