They are top-secret, tough guys who won't even admit they exist.

But the exploits of the men in the U.S. Navy SEALs' Team Six — the Naval Special Warfare Development Group — made headlines around the world after they dropped out of the sky into a fortified compound in Pakistan and fatally shot Osama bin Laden  in the head.

About two dozen SEALs from the elite military counterterrorism unit wearing night-vision goggles stormed the compound and left about three-quarters of an hour later with bin Laden's body.

Their names may never be known.

"A lot of these missions — a majority of these missions — are ones that the public will never know about … and that's a good thing," SEAL spokesman Capt. Duncan Smith told ABC News.

U.S. Navy Sea, Air and Land teams trace their origins to the scouts, raiders, underwater demolition teams, office of strategic services operational swimmers and other elite groups specializing in unconventional warfare that were set up to do beach reconnaisance and preparation for amphibious landings in the Second World War. The first official SEAL teams were set up in 1962. According to the  U.S. Navy SEAL website, two SEAL teams were formed from the existing underwater demolition teams and given the mandate to "conduct counter guerilla warfare and clandestine operations in marine and riverine environments."

Over the years, the SEALs have been deployed in various configurations to conduct raids, assaults and reconnaissance missions in numerous conflicts, including in Vietnam, the Persian Gulf, Bosnia, Haiti, Somalia and, most recently, Afghanistan and Iraq.

'Black' operatives

Technically, Team Six doesn't exist. Its highly trained members are so-called black operatives who work outside military protocol on top-secret missions and often act outside the boundaries of international law, according to a report on the Business Insider website.

The SEAL Team Six was created in response to the failed 1980 attempt to rescue U.S. hostages in Iran, Business Insider reported.

The group was initially called Team Six in an effort to confuse Soviet intelligence about the number of SEAL teams in operation — two, Business Insider said.

About 2,500 SEALs were on active duty as of 2009, ABC News reported.

But none of them could just sign up to be a member of Team Six if they took a notion. Instead, its members are recruited from active SEAL teams. It's not a mission for everyone.

'You just have to dig deep'

"You have to be able to endure a lot of physical pain and sometimes emotional pain, and you just have to dig deep," Paul Tharp, master chief of the Naval Special Warfare Preparatory School and a SEAL for 24 years, told ABC News. "It's an elite organization, and so it can't be for everybody."

Members can't even tell anyone about their job.

"You know I'd love to help you man," a former Navy SEAL told Business Insider, "but I can't say a word about Team Six. There is no Team Six."