Since then, Delta Force has quietly done its job, developing an ethos, top military commanders say, of competence that is second to none in the military. The culture of Delta Force “has been one of humility versus bravado, of quiet professionalism rather than seeking publicity, and not revealing their methods to protect both themselves as well as those they seek to help,” said Wade Ishimoto , a retired Army officer who took part in the Iran rescue mission.

In October 1993 , Delta Force commandos were alongside Army Rangers in what would later become known as the Black Hawk Down incident in Somalia. The pitched daylong battle left more than a dozen Americans dead. The bloody outcome, according to a former Special Operations officer who has worked closely with both Delta Force and SEAL Team 6 , highlighted the need for greater professionalization and a stronger officer corps to help avoid similar failures. Delta’s stronger officer corps is one reason it has avoided some of the high-profile missteps of its Navy counterpart, the officer suggested.

In 2011, Delta Force was originally selected to carry out the raid against Bin Laden in Pakistan, according to two Defense Department officials. But they were waved off when military officials determined that the presence of Delta Force commandos in Afghanistan, where normally SEAL Team 6 was operating at the time, would cause consternation among those in country and could possibly reveal the American hand before the attack.

So that marquee task went to SEAL Team 6. In one way, it turned out to be the worse thing that happened to them, as the raid not only put the spotlight on an organization that was supposed to be secret, but also fed a mythology that led to book deals and movies and a thinking among many SEALs that they were above the Uniform Code of Military Justice. Those actions left the historically more tight-lipped Delta Force troops rolling their eyes.

Members of both units are expected to honor a code of silence about their missions, and many current and former SEAL Team 6 members fume that two of their own spoke out about their role in the Qaeda leader’s death. The men, Matt Bissonnette, author of two best sellers about his tenure at SEAL Team 6, and Robert O’Neill , who said in a television special that he had killed Bin Laden, were investigated by the Naval Criminal Investigative Service over accusations that they revealed classified information.