Explorer II was a manned U.S. high-altitude balloon that was launched on November 11, 1935, and reached a record altitude of 22,066 m (72,395 ft). Launched at 8:00 am from the Stratobowl in South Dakota, the helium balloon carried a two-man crew consisting of U. S. Army Air Corps Captains Albert W. Stevens and Orvil A. Anderson inside a sealed, spherical cabin. The crew landed safely near White Lake, South Dakota, at 4:13 pm and both were acclaimed as national heroes. Scientific instruments carried on the gondola returned useful information about the stratosphere. The mission was funded by the membership of the National Geographic Society.
In January 1934, the National Geographic Society (NGS) and the U. S. Army Air Corps decided to collaborate on a program to build and launch a manned balloon to the then record altitude of 24 km (15 mi). This vehicle would be capable of carrying a crew of three in an airtight capsule, along with a laboratory of instruments. The hydrogen balloon, named Explorer, was completed by July at a cost of around $60,000; equivalent to $1,215,373 in 2021 currency.
The balloon was launched from a canyon in the Black Hills of South Dakota—dubbed the Stratobowl—on July 28, 1934 and reached a near-record altitude of 18,475 m (60,613 ft) before tears in the fabric led the crew to begin reducing their altitude. A rupture in the balloon resulted in a precipitous descent, followed by a spark that caused the hydrogen to ignite and destroy what was left of the balloon, leaving the capsule to plummet toward the ground at terminal velocity. The crew just managed to escape using their parachutes, with the last man bailing out at 500 feet (150 m) above the ground. Their capsule was almost completely destroyed upon impact.