American B-52 bombers and Spectre gunships bristling with cannon have been sent into action against the Taliban in an attempt to stop the insurgents’ march on three key cities in Afghanistan.

The return of the massive B-52 “stratofortress”, after at least a year’s hiatus, is the clearest sign that the Pentagon is being forced to launch heavyweight daily assaults, not only to halt the Taliban but also to aid the US-trained Afghan air force as it struggles to cope with unprecedented demand for its services.