In addition to the usual Apollo spacecraft training, Young and Duke, along with backup commander Fred Haise, underwent an extensive geological training program that included several field trips to introduce them to concepts and techniques they would use in analyzing features and collecting samples on the lunar surface. During these trips, they visited and provided scientific descriptions of geologic features they were likely to encounter. The backup LMP, Mitchell, was unavailable during the early part of the training, occupied with tasks relating to Apollo 14, but by September 1971 had joined the geology field trips. Before that, Tony England (a member of the support crew and the lunar EVA CAPCOM) or one of the geologist trainers would train alongside Haise on geology field trips. Since Descartes was believed to be volcanic, a good deal of this training was geared towards volcanic rocks and features, but field trips were made to sites featuring other sorts of rock. As Young later commented, the non-volcanic training proved more useful, given that Descartes did not prove to be volcanic. In July 1971, they visited Sudbury, Ontario, Canada, for geology training exercises, the first time U.S. astronauts trained in Canada. The Apollo 14 landing crew had visited a site in West Germany; geologist Don Wilhelms related that unspecified incidents there had caused Slayton to rule out further European training trips. Geologists chose Sudbury because of a wide crater created about 1.8 billion years ago by a large meteorite. The Sudbury Basin shows evidence of shatter cone geology, familiarizing the Apollo crew with geologic evidence of a meteorite impact. During the training exercises the astronauts did not wear space suits, but carried radio equipment to converse with each other and England, practicing procedures they would use on the lunar surface. By the end of the training, the field trips had become major exercises, involving up to eight astronauts and dozens of support personnel, attracting coverage from the media. For the exercise at the Nevada Test Site, where the massive craters left by nuclear explosions simulated the large craters to be found on the Moon, all participants had to have security clearance and a listed next-of-kin, and an overflight by CMP Mattingly required special permission. In addition to the field geology training, Young and Duke also trained to use their EVA space suits, adapt to the reduced lunar gravity, collect samples, and drive the Lunar Roving Vehicle.