As for the pilots who would go on to participate in the attacks, three of them were original members of the Hamburg cell (Mohamed Atta, Marwan al-Shehhi and Ziad Jarrah). Following their training at al-Qaeda training camps in Afghanistan, they were chosen by Bin Laden and al-Qaeda's military wing due to their extensive knowledge of western culture and language skills, increasing the mission's operational security and its chances for success. The fourth intended pilot, Ramzi bin al-Shibh, a member of the Hamburg cell, was also chosen to participate in the attacks yet was unable to obtain a visa for entry into the United States. He was later replaced by Hani Hanjour, a Saudi national.