The newly promoted four-star general, Keith Alexander, takes charge of the Pentagon's new Cyber Command, designed to conduct virtual combat across the world's computer networks.
The creation of the US' most senior cyber warrior comes just days after the US air force disclosed that some 30,000 of its troops had been re-assigned from technical support "to the frontlines of cyber warfare".
The creation of Cyber Command is in response to increasing anxiety over the vulnerability of the US' military and other networks to a cyber attack.
James Miller, the deputy under-secretary of defence for policy, has hinted that the US might consider a conventional military response to certain kinds of online attack.
Although Alexander pledged during his confirmation hearings before the Senate committee on armed services last month that Cyber Command would not contribute to the militarisation of cyberspace, the committee's chairman, Senator Carl Levin expressed concern that both Pentagon doctrine, and the legal framework for online operations, had failed to keep pace with rapid advances in cyber warfare.
While Alexander has tried to play down the offensive aspects of his command, the Pentagon has been more explicit, stating that Cyber Command will "direct the operations and defence of specified Department of Defense information networks [involving some 90,000 military personnel] and prepare to, when directed, conduct full-spectrum military cyberspace operations in order to enable actions in all domains, [to] ensure US allied freedom of action in cyberspace and deny the same to our adversaries".