But video obtained exclusively by CBS News shows a look at what some have been doing on the job, CBS News correspondent Sharyl Attkisson reports.
They've been sleeping.
Inside the so-called "ready room" at Peach Bottom Nuclear Plant in Pennsylvania, the guards hardly seem ready to intercept an adversary.
Attkisson spoke to a guard about what he'd seen. How many people did one personally witness sleeping on the job?
"I'd say about 20," he said.
CBS News spoke to two former Wackenhut employees. One was a guard, the other a security force manager. Neither wants to be identified, for fear of retaliation.
The two guards shown in video as being sound asleep, were they armed?
"Absolutely," a guard said.
What kind of guns do they have?
"Machine guns," he said.
Hired by Wackenhut in January, one guard says he was stunned that co-workers routinely slept on duty - not just in the "ready room," but in the bulletproof watch towers, too.
"Anytime I would go to discuss this with a supervisor, I was told that, 'hey, don't talk about that. Focus on being a team player,'" he explained.
In his mind, what did they mean when they said he should be a team player?
"That it's socially acceptable," he said.
"Yeah, it's the culture there to do it," he said.
They even notified the Nuclear Regulatory Commission, but nothing changed. So the guard decided to use his cell phone and camera to get evidence.
They videotaped napping in March … still at it in June ... and getting more shuteye in August.
Wackenhut, which heads up security at 29 nuclear plants, wouldn't agree to an interview. But Friday, they did send CBS News two press releases.
One former Wackenhut security force manager says the snoozing wasn't isolated.
Press release: Wackenhut Expedites Corrective Actions as Investigation Continues (1 page).
Wackenhut Charts New Strategic Direction for Nuclear Services Division (2 pages).
Attkisson asked: "Is there any doubt in your mind that Wackenhut managers have known for a long time that there are officers sleeping not just at Peach Bottom but at other places too?
"In my experience, I think I can clearly say that they absolutely did know," the former manager said.
Reports of sleeping guards have hounded Wackenhut for years.
Just this week, the Nuclear Regulatory Commission confirmed the same problem at Florida's Turkey Point Nuclear Plant from 2004-2006. Multiple Wackenhut guards were "inattentive" or served as "lookouts" for others.
But that hasn't affected the company's ability to get hundreds of millions of your tax dollars to protect some of the most sensitive government sites in the nation.
NRC letter regarding the investigation into employee inattentiveness (2 pages).
Factual summary of the report (1 page).
That includes a $549 million contract to guard the federal Y-12 complex - a prime target for terrorists because it stores tons of highly-enriched uranium.
Only after the embarrassing video surfaced in a story broken by WCBS in New York did federal investigators finally swoop in.
"My family's life is in danger," a guard said. "My friends' families' lives are in danger. Something had to be done."
Peach Bottom hired some of the former Wackenhut guards for its new security force, but not the man behind the camera who cared so much about public safety that he blew the whistle. He was told he doesn't meet the criteria for the job.