While I know full well that it is considered un-American to admit defeat before the battle is even engaged, attempting to fight tanks with bare fists is pure folly. But we're talking about serious stakes here. All of these activities are highly interdependant and highly computerized. Financial firms move money by telephone, not by armored car. Without communications, financial institutions quickly grind to a halt.
Communications companies depend upon electricity, and so forth.
Disruption in these civilian resources would directly affect the DoD's ability to fulfill its missions. Just as any significant disruptions of communications, transportation and energy would likewise seriously cripple any organization from conducting it's normal business. By no means am I saying that rolling computer failures will mean the end of modern society as some critics have claimed. What I do believe is that, as a global interdependant society, we are extremely ill prepared to cope with what may happen. If we actively consider and prepare for worst case scenarios, then actually weathering the inevitable storms will be far easier.