On May 5, 1961, Navy Commander Alan Bartlett Shepard Jr. 
was launched into space aboard the Freedom 7 space capsule,
becoming the first American astronaut to travel into space.

Shepard and Freedom 7 on the deck of the aircraft carrier
USS Lake Champlain.

Alan Bartlett Shepard Jr. (1923 – 1998)

Osama bin Laden, the mastermind behind the September 11,
2001, terrorist attacks in the United States, was killed by U.S.
forces during a raid on his compound hideout in Pakistan.

The notorious, 54-year-old leader of Al Qaeda, the terrorist
network of Islamic extremists, had been the target of a nearly
decade-long international manhunt.

The raid began around 1 a.m. local time (4 p.m. EST on May 1,
2011 in the United States), when 23 U.S. Navy SEALs in two
Black Hawk helicopters descended on the compound in
Abbottabad, a tourist and military center north of Pakistan’s
capital, Islamabad. One of the helicopters crash-landed into
the compound but no one aboard was hurt.

During the raid, which lasted approximately 40 minutes, five
people, including bin Laden and one of his adult sons, were
killed by U.S. gunfire. No Americans were injured in the assault.

A vendor walks past a sand sculpture of al-Qaeda leader
Osama bin Laden created by Indian sand artist Sudarshan Patnaik on a beach in Puri in the eastern Indian state of
Orissa on May 2, 2011. (Reuters)

On April 24, 1980, an ill-fated military operation to rescue
the 52 American hostages held in Tehran ended with eight
U.S. servicemen dead and no hostages rescued.

With the Iran Hostage Crisis stretching into its sixth month
and all diplomatic appeals to the Iranian government ending
in failure, President Jimmy Carter ordered the military mission
as a last ditch attempt to save the hostages.

The next day, a somber Jimmy Carter gave a press conference
in which he took full responsibility for the tragedy. The hostages
were not released for another 270 days.

President Carter flew to West Germany to greet the Americans
on their way home.

On April 20, 1999, two teenage gunmen killed 13 people in a
shooting spree at Columbine High School in Littleton,
Colorado, south of Denver.

By 11:35 a.m., Klebold and Harris had killed 12 fellow students
and a teacher and wounded another 23 people. Shortly after
noon, the two teens turned their guns on themselves and died
by suicide.

The crime prompted a national debate on gun control and
school safety, as well as a major investigation to determine
what motivated the teen gunmen.    
  

In the days immediately following the shootings, it was
speculated that Klebold and Harris purposely chose jocks,
minorities and Christians as their victims.         

Harris (left) and Klebold (right) in the cafeteria.

On April 16, 2007, 32 people died after being gunned down
on the campus of Virginia Tech by Seung-Hui Cho, a student
at the college who later died by suicide.

The Virginia Tech shooting began around 7:15 a.m., when
Cho, a 23-year-old senior and English major at Blacksburg-
based Virginia Polytechnic Institute and State University,
shot a female freshman and a male resident assistant in a
campus dormitory before fleeing the building.

Police were soon on the scene; unaware of the gunman’s
identity, they initially pursued the female victim’s boyfriend
as a suspect in what they believed to be an isolated domestic-
violence incident.

However, at around 9:40 a.m., Cho, armed with a 9-millimeter
handgun, a 22-caliber handgun and hundreds of rounds of
ammunition, entered a classroom building, chained and locked
several main doors and went from room to room shooting
people. Approximately 10 minutes after the rampage began,
he died from a self-inflicted gunshot wound.

The attack left 32 people dead and more than a dozen wounded.

Cho Seung-hui, the Virginia Tech gunman who killed 32
people before turning the gun on himself. Photograph:
AP