The highly trained operatives who killed Osama bin Laden are part of a counterterrorism group so specialized that no one can apply to join it.

Instead, they are recruited. They are chosen from existing SEAL teams, making the unit an elite within an elite.

Authoritative information on the secretive unit is hard to come by, but several websites dedicated to military affairs agree on some basic information.

The group was originally known as Team Six, but the official name was changed in 1987 to the Naval Special Warfare Development Group.

While most information relating to the group is classified, it is believed to have been formed in response to the failed 1980 attempt to rescue American hostages in Iran. Richard Marcinko was its first commander.

The unit is a component of the Joint Special Operations Command, which also oversees the Army's Delta Force.

It has operated in Somalia, the former Yugoslavia, Afghanistan and Iraq. Members have hunted down key al-Qaeda and Taliban figures since 2001.

Members are not allowed to talk about any aspect of the group still commonly known as Team Six.

A former Navy SEAL contacted by Business Insider told the website: "You know I'd love to help you man, but I can't say a word about Team 6. There is no Team 6."

The Associated Press contributed to this article.