Last week US defence chiefs unveiled their plan for battling global Islamist extremism. They envisage a conflict fought in dozens of countries and for decades to come. Today we look in detail at this seismic shift in strategic thinking, and what it will mean for Britain

The message from General Peter Pace, the chairman of the US joint chiefs of staff, was apocalyptic. "We are at a critical time in the history of this great country and find ourselves challenged in ways we did not expect. We face a ruthless enemy intent on destroying our way of life and an uncertain future."

Gen Pace was endorsing the Pentagon's four-yearly strategy review, presented to Congress last week. The report sets out a plan for prosecuting what the the Pentagon describes in the preface as "The Long War", which replaces the "war on terror". The long war represents more than just a linguistic shift: it reflects the ongoing development of US strategic thinking since the September 11 attacks.

Looking beyond the Iraq and Afghan battlefields, US commanders envisage a war unlimited in time and space against global Islamist extremism. "The struggle ... may well be fought in dozens of other countries simultaneously and for many years to come," the report says. The emphasis switches from large-scale, conventional military operations, such as the 2003 invasion of Iraq, towards a rapid deployment of highly mobile, often covert, counter-terrorist forces.

Among specific measures proposed are: an increase in special operations forces by 15%; an extra 3,700 personnel in psychological operations and civil affairs units - an increase of 33%; nearly double the number of unmanned aerial drones; the conversion of submarine-launched Trident nuclear missiles for use in conventional strikes; new close-to-shore, high-speed naval capabilities; special teams trained to detect and render safe nuclear weapons quickly anywhere in the world; and a new long-range bomber force.