Houston. Fires were set aboard a boilerplate CM using various atmospheric compositions and pressures. The results led to the decision to use 60 percent oxygen and 40 percent nitrogen within the CM at launch, which would be replaced with a lower pressure of pure oxygen within four hours, as providing adequate fire protection. Other boilerplate spacecraft were subjected to drops to test parachutes, and to simulate the likely damage if a CM came down on land. All results were satisfactory. During the run-up to the mission, the Soviets sent uncrewed probes Zond 4 and Zond 5 (Zond 5 carried two tortoises) around the Moon, seeming to foreshadow a circumlunar crewed mission. NASA's Lunar Module (LM) was suffering delays, and Apollo Program Spacecraft Manager George Low proposed that if Apollo7 was a success, that Apollo 8 go to lunar orbit without a LM. The acceptance of Low's proposal raised the stakes for Apollo7. According to Stafford, Schirra "clearly felt the full weight of the program riding on a successful mission and as a result became more openly critical and more sarcastic." Throughout the Mercury and Gemini programs, McDonnell Aircraft engineer Guenter Wendt led the spacecraft launch pad teams, with ultimate responsibility for condition of the spacecraft at launch. He earned the astronauts' respect and admiration, including Schirra's. However, the spacecraft contractor had changed from McDonnell (Mercury and Gemini) to North American (Apollo), so Wendt was not the pad leader for Apollo1. So adamant was Schirra in his desire to have Wendt back as pad leader for his Apollo flight, that he got his boss Slayton to persuade North American management to hire Wendt away from McDonnell, and Schirra personally lobbied North American's launch operations manager to change Wendt's shift from midnight to day so he could be pad leader for Apollo7. Wendt remained as pad leader for the entire Apollo program. When he departed the spacecraft area as the pad was evacuated prior to launch, after Cunningham said, "I think Guenter's going", Eisele responded "Yes, I think Guenter went." Hardware Spacecraft The Apollo 7 spacecraft included Command and Service Module 101 (CSM-101) the first BlockII CSM to be flown. The BlockII craft had the capability of docking with a LM, though none was flown on Apollo7. The spacecraft also included the launch escape system and a spacecraft-lunar module adapter (SLA, numbered as SLA-5), though the latter included no LM and instead