The US Defence Department has released a long-awaited report on how the US military will organise and equip itself in the face of "new and elusive foes".
The report says the US must gear up for prolonged warfare
The quadrennial defence review will be presented to the US Congress next week.
The document, known by its acronym, QDR, opens with the words: "The US is engaged in what will be a long war."
It describes what the US military must do to defeat current and future enemies - flagged as "rogue powers, terrorist networks and non-state threats".
The document identifies four categories of threat:
- Traditional challenges - other nation states fielding conventional militaries which will compete with the US
- Irregular challenges - terrorism and insurgency chief among them
- Catastrophic challenges - the use of weapons of mass destruction by international terrorist networks or "rogue states"
- Disruptive challenges - an enemy's ability to counter or interfere with US capabilities, perhaps through new technologies
Of these, say the authors of the quadrennial defence review (QDR), the catastrophic challenge is the most serious threat, and the one which the US must work most assiduously to address.
The review plans for more special operations forces that can operate anywhere in the world at short notice and in secret.
Some independent analysts in Washington are already asking how the military plans to pay for all these changes
It also foresees better intelligence, and more unmanned aircraft that can loiter and spy and attack.
It will deploy more soldiers in psychological warfare and stability operations.
It will build special units that can track and disable nuclear weapons.
These are all capabilities, says the military, aimed at fighting an enemy like al-Qaeda in the information age - very different to fighting another country in the industrial age.
In this, the QDR highlights a moment of historical transition: a moment when infantry divisions, battleships and artillery began to fade as the truest instruments of military power.
It is a moment when intelligence and surveillance mechanisms, agile, self-sufficient combat brigades and unmanned aircraft began to come of age.
Some fundamental strategic goals don't seem to have changed. The review specifies that America should still be able to fight two conventional wars almost simultaneously.
Unmanned aircraft could become a hallmark of future US warfare
But it says the military must also gear itself to fight prolonged, irregular warfare, like that in Iraq.
The principal Undersecretary of Defence for Policy, Ryan Henry, said that the QDR had been shaped by lessons learned since 11 September 2001.
And the one constant in US defence planning was that America's enemies had become highly unpredictable.
"I can tell you now that US forces in all probability will be engaged somewhere in the world in the next decade where they're not currently engaged," he said.
"But I can tell you with no resolution at all where that might be, when that might be or how that might be. And that's indicative of the uncertainty that we face," he added.
This thinking is not new. And Mr Henry stressed that the QDR was not "a new beginning" for the US military.
Rather, it was a part of a "continuum" of change.
But the document does give a clear explanation of America's strategic direction. And for a document produced by the Pentagon, it's surprisingly free of unintelligible jargon.
Question of cost
Some independent military analysts professed themselves under-whelmed, however.
"Overall, the 2005 QDR fell far short of its objectives," wrote Michele A Flournoy, who was a Pentagon official in the Clinton administration, and is now at the Center for Strategic and International Studies.
"Rather than being 'a fulcrum of transition to a post-September 11 world'... as was originally anticipated, the QDR made only a few significant adjustments to the US defence programme," she wrote.
The document does not, as some expected, call for cuts in big conventional weapons programmes, like the development of a new war plane known as the joint strike fighter, or a new destroyer for the navy.
Given that, some independent analysts in Washington are already asking how the military plans to pay for all these changes.
That question may get some sort of answer next week when the Pentagon requests its annual budget from Congress.
This year's budget is expected to be about $440bn (£250bn), and that doesn't include the cost of the wars in Afghanistan and Iraq.