Warfare is changing. Amid the historical questions shrouding the 10th anniversary of the September 11 attacks - America's troubled place in the world and the ultimate costs to the US of its responses to al-Qaeda's fateful strike - the changing face of modern warfare is far more certain.
Then president George W. Bush's 'war on terror' - dismissed in some quarters as a dangerously misguided war on a tactic, rather than a defined enemy - has evolved dramatically over the past decade. It has moved beyond the invasions of Afghanistan and Iraq into a ruthlessly efficient campaign of 'targeted killings' of al-Qaeda operatives, barely conceivable just a few years ago.
This element of the conflict is a continual war without a front line or massed ranks of a uniformed enemy; the hunt for a 'non-state actor', against which conventional weaponry and armour are of questionable value. Instead, it is a conflict fought at the nexus of intelligence operations and analysis, the law and the latest in precision military technology - a new world that makes the niceties of the Geneva Conventions of 1949, conceived in a time of prisoner-of-war camps and Red Cross food parcels, appear out of date, if not obsolete.
At its secretive heart is the US Joint Special Operations Command - an expanded elite cadre of Washington's more creative military leaders and special forces units. Linked to America's vast intelligence establishment, particularly the CIA, it works closely with the executive branch - including the White House - in a reflection of its political importance and legal delicacy.
The command's most high-profile action was its raid in May on the fortified mansion hiding Osama bin Laden and his family in the Pakistani town of Abbottabad. Less visible than the killing of bin Laden, however, are its ongoing operations in not only Afghanistan and Pakistan's mountainous tribal hinterlands, but also Yemen and Somalia. The command maintains a list of the most wanted terrorists, hunting them in covert raids by US Navy SEALS, as well as missile strikes by unmanned drone aircraft operated by the CIA and/or the US Air Force.
The use of drones - unmanned aerial vehicles (UAVs), as they are officially known - is arguably the most potent example of the way the US war on al-Qaeda is changing modern warfare.
A study by the New America Foundation, a Washington think tank, highlights how the Bush era's pioneering use of drones has rapidly expanded under the presidency of Barack Obama.