The September 11, 2001 attacks were a series of coordinated suicide attacks by al-Qaeda upon the United States on September 11, 2001.

On that morning, 19 Islamist terrorists affiliated with al-Qaeda hijacked four commercial passenger jet airliners. The hijackers intentionally crashed two of the airliners into the Twin Towers of the World Trade Center in New York City, killing everyone on board and many others working in the buildings. Both buildings collapsed within two hours, destroying at least two nearby buildings and damaging others. The hijackers crashed a third airliner into the Pentagon. The fourth plane crashed into a field near Shanksville in rural Somerset County, Pennsylvania, after some of its passengers and flight crew attempted to retake control of the plane, which the hijackers had redirected toward Washington, D.C. There are no survivors from any of the flights.

Excluding the 19 hijackers, 2,974 people died in the attacks. The overwhelming majority of casualties were civilians, including nationals of over 90 different countries. In addition, the death of at least one person from lung disease was ruled by a medical examiner to be a result of exposure to dust from the World Trade Center's collapse.

The United States responded to the attacks by launching a "War on Terrorism", invading Afghanistan to depose the Taliban, who had harbored al-Qaeda terrorists, and enacting the USA PATRIOT Act. Many other states also strengthened their anti-terrorism legislation and expanded law enforcement powers. Some American stock exchanges stayed closed for the rest of the week, and posted enormous losses upon reopening, especially in the airline and insurance industries. The destruction of billions of dollars worth of office space caused the economy of Lower Manhattan to grind to a halt.

The damage to the Pentagon was cleared and repaired within a year, and the Pentagon Memorial was built on the site. The rebuilding process has started on the World Trade Center site. In 2006 a new office tower was completed on the site of 7 World Trade Center. The 1 World Trade Center is currently under construction at the site and at 1,776 ft (541 m) upon completion in 2011, will become one of the tallest buildings in North America. Three more towers are expected to be built between 2007 and 2012 on the site.(courtesy Wikipedia)

The Striking of the "Four Fives"

Long before radios and pagers FDNY used the fire alarm telegraph system to announce the line of duty death of a firefighter. The signal 5-5-5-5 was transmitted over both primary and secondary circuits. When fire trucks became equipped with radios, the telegraph signal would be followed up with a radio announcement: "It is with regret that announcement is made of the death of ..."