Al Qaeda has a strong track record over the years of returning to targets or types of targets it has attacked in the past, regardless of whether the initial attack was successful. This pattern, which includes transportation targets, suggests that the July 7 London bombings will not be the last attack against a Western subway system. In October 2000, after an unsuccessful attempt against the USS The Sullivans, a U.S. Navy destroyer, al Qaeda militants succeeded in attacking another ship, the USS Cole, while it was anchored in Aden harbor in Yemen for refueling. Seventeen U.S. sailors died in the attack. In 1996, an al Qaeda operation targeted the Khobar Towers U.S. Air Force dormitory near Dhahran, Saudi Arabia, killing 19 U.S. airmen. Using the same tactic two years later, al Qaeda operatives successfully attacked U.S. embassies in Kenya and Tanzania, killing at least 252 people and injuring thousands. In both cases, the targets were large buildings and the attackers employed truck-borne improvised explosives. The most striking example of the al Qaeda pattern is the double attack against the World Trade Center. Although they used different tactics, the perpetrators of both the 1993 and the 2001 attacks were attracted to the target for the same reasons: The towers' significant symbolic appeal and the potential for a high casualty count. In most cases, terrorists look for the likelihood of causing mass casualties as one of their criteria in selecting a target. Because subways are compact, they concentrate the force of any explosion — meaning the attackers can get by with smaller, less-powerful bombs and still kill or maim many people. In addition to the death and destruction caused by the explosion itself, smoke inhalation would claim more victims. Compounding this is the fact that subways are sealed systems, with few entry and exit points, making escape difficult. This was shown to good effect in the 1995 sarin gas attack against the Tokyo subway by the Japanese apocalyptic cult Aum Shinrikyo, which killed 12 people and sent about 5,000 to the hospital. For this reason, the New York subway system has been the target of several terrorist plots in the past, and there is no reason to believe that militants will refrain from targeting it in the future. STRATFOR has long pointed out this threat. On July 31, 1997, Palestinians Gazi Ibrahim Abu Mezer and Lafi Khalil were arrested for conspiring to detonate several bombs in the Atlantic Avenue subway station in Brooklyn, N.Y. One of their associates, Abdul Rahman Mossabah, an Egyptian who had been in the United States for just two weeks, alerted police to the plot the day before it was to take place. When police raided their dwelling, one of the two apparently attempted to detonate a bomb, but police shot and wounded the two men. Five pipe bombs and one apparent suicide bomb were recovered. Abu Mezer was convicted on three counts of a four-count federal indictment and sentenced to life in prison. Khalil, convicted on one count, was sentenced to 36 months in prison. In August 2004, Shahawar Matin Siraj and James Elshafay were arrested for conspiring to place explosives in the 34th Street subway station in Manhattan. Their plot was uncovered by a confidential informant they believed was going to provide them with the needed explosives. Both men await trial in U.S. federal court facing a maximum sentence of 20 years imprisonment if convicted. Encouraged by the successful attacks against the London Underground and on the Madrid trains in March 2004, al Qaeda can be expected to continue to target Western commuter rail systems, especially subways.