A few weeks ago I was standing by a railway track in the small town of Gaithersburg in Maryland as a CSX freight train blasted through the level crossing; its horn blaring and bells sounding out a warning.
Passengers may have largely deserted America's rails but freight trains remain vital to America's economic well-being.
Like most other pieces of modern infrastructure the railways are controlled by complex digital systems. And there are growing fears that these computers could fall prey to cyber-attack, as could all the other electronic support systems on which modern society now depends.
Last year the then US defence secretary Leon Panetta spoke of the possibility of a possible "digital Pearl Harbor"; a massive attack that might target US transport infrastructure and utilities.
Just a few weeks ago in his State of the Union address President Barack Obama added his own warning.
"We know hackers steal people's identities and infiltrate private emails," he said. "We know foreign countries and companies swipe our corporate secrets," he went on, "now our enemies are also seeking the ability to sabotage our power grid, our financial institutions, our air traffic control systems."
Hundreds of private companies are springing up to respond to the possibility of a digital doomsday.
The stakes are high as Shawn Henry told me. "Other than a weapon of mass destruction going off in a major city," he says, "the cyber-threat is one of the most significant challenges that we face."
Mr Henry is a former executive assistant director of the FBI - he was responsible for its cyber-investigations worldwide.
He is now president of Crowdstrike, a company which helps firms protect against hackers.
"Everything we do day-to-day relies on cyber-communications," he said.
"All of our data that's being pushed to the network or financial services sector, our critical infrastructure, our electric power grid, our water systems.
"We know with certainty that there are groups that are actively seeking to target and harm the western world through attacks on the cyber-network.
"If that happens I think we are going to suffer some significant consequences."
Hurricane Katrina in 2005 showed how quickly a sophisticated society can start to break down once key services are destroyed. The Secretary of Homeland Security at the time of the hurricane, Michael Chertoff, told me that the threat from cyber-attack is very real.
He said: "Even now as we speak there are millions of attacks every day on infrastructure, simply stealing information or stealing intellectual property.
"Now, the same capability that allows somebody to do that is a capability that allows someone to be destructive. So yes it is a distinct possibility that systems that are connected to the internet, if they control operations, could be damaged or destroyed."
In the US State of New Jersey, Ed Skoudis is preparing for the possibility of just such a catastrophe. His office is filled with extravagant curios - it's Jules Verne meets Steam-Punk - there's a turn of the century phonograph, reproductions of early light bulbs, and in the basement, a model train set.
But this model railway is no toy. Along with a battery of supporting computers it's used by government agencies and private companies to simulate what could happen if hackers tried to take control of a town's digital infrastructure.
"We built Cyber City," Skoudis told me, "so that there's actually 15,000 inhabitants… and the inhabitants aren't like physical little people, but instead they're actually data - they have hospital records, they have family relationships, so you can see that this person is related to that person.
"They have bank records, they have accounts on our social networking site… and cyber-warriors will look at these different relationships and try to discern things that they can use in their defence and attack against the city,"
It's a miniaturised visualisation of a digital training range and it is getting a good deal of use.
The language of the cyber-warriors is certainly apocalyptic. But amid shrinking defence budgets some believe the cyber-threat has been exaggerated. Thomas Rid, a reader in War Studies at King's College London, is blunt about how he views the true extent of the threat. The title of his new book is - Cyber War Will Not Happen.
"I think the scenario of a cyber Pearl Harbor or sometimes even a cyber 9/11 is an overstatement," he told me.
"In fact if you talk to Pentagon officials on background. They may actually admit that such statements are overstated because it's useful for political reasons, to put pressure on Congress to pass cybersecurity legislation."
Ed Skoudis acknowledges that there is a lot of "cyber-hype" around. But he insists that there are still real dangers out there. "There is something real behind all this," he said.
"We are seeing successful attacks where bad guys gain control of elements within the power grid, or other critical infrastructures, and they could use that to take serious action. There is hype," he adds, "but there's a core nugget to this where you can take action via cyber-means to have military effects."
This fear of a destructive cyber-threat is pushing the United States to bolster its defences - the Pentagon is recruiting 4000 new cyber-warriors.
A new presidential order has been signed to better protect America's critical infrastructure from hackers. Protecting against the risk of digital attack is a rapidly expanding industry - one in which the military and private companies are aggressively competing to claim their share.