Largo, Florida (CNN) Ret. Sgt. Tom Block is sitting in the classroom, looking restless. He and 23 other highly specialized, highly coveted candidates are all vying for a job where they will be exposed to some of the most horrifying images humanity can produce. 
 
 Each candidate is a veteran of America's recent wars. Many were part of the elite special ops forces. They conducted daring, covert missions to take out America's most dangerous enemies. 
 
 Many were wounded in battles across Afghanistan and Iraq. And now that their military career has come to a close, they are looking for a second chance to find purpose in their lives back at home -- and the answer could be the HERO Child-Rescue Corps, saving at risk kids. 
 
 J. Christian, CEO of the National Association to Protect Children (Protect) , says: "A lot of the individuals who come into the HERO Corps are truly individuals who have lost their mission on the battlefield." 
 
 Christian, an Army Ranger who fractured his spine during a mission in Afghanistan, says many of the veterans who come into HERO are hoping to regain that something they lost when they left the service. 
 
 Block is hoping to get a second chance to "go after bad guys again." 
 
 "In one second their entire life changed. When that happens, I know from personal experience, you start to wonder, what can I now do? And once you find this opportunity, you know it's truly your opportunity to step back into that role." 
 
 The HERO -- Human Exploitation Rescue Operative -- program is designed for wounded, injured and ill veterans to receive training in sophisticated computer forensics, to join federal agents fighting against online child sexual exploitation. 
 
 Developed by Protect, in conjunction with Homeland Security Investigations (HSI) and U.S. Special Operations Command (SOCOM), the veterans receive 11 weeks of intensive training and 10 months of on-the-ground experience. 
 
 They work alongside law enforcement teams executing warrants and serving as computer forensic analysts as part of a year-long unpaid internship. That means scanning computers and external hard drives on-site to determine whether the suspect possesses child pornography and, critically, whether the suspect is also producing child pornography. 
 
 During that year-long internship, HERO Corps trainees will sift through thousands of disturbing images of adults sexually assaulting children. 
 
 "You see groups of children being abused at levels the average American cannot fathom. If you imagine an infant getting gagged and bound and tortured, it's not a rare occurrence to come across," says Christian. 
 
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 According to Christian, the U.S. is the largest producer of child pornography in the world. He also points to research showing the U.S. is home to the most commercial child porn websites 
 
 The National Center for Missing and Exploited Children says its Victim Identification Program, which aids law enforcement in efforts to locate and rescue child victims, has reviewed more than 158 million images and videos , since 1998. 
 
 In 2008, an ICAC Task Force network identified over 300,000 unique computers engaged in trafficking child pornography . A study by the University of New Hampshire found that 55 percent of those who possess or trade child pornography, are hands-on offenders. 
 
 Block says: "It's horrible. But that's my motivation, that's my drive. To get after these guys. Get them off the internet and hopefully I can get to them before they get to another child." 
 
 Now in its third year, HERO Corps hopes to place its 100th veteran this year. Once embedded in a law enforcement agency, just one HERO can stop or prevent the exploitation of as many as 50 children per year, by providing law enforcement with the digital evidence they need to identify and locate endangered children. 
 
 Cpl. Justin Gaertner (left) and Sgt. Gabe Martinez (right) were both injured in action, both are amputees in wheelchairs and both are joining HERO Corps. 
 
 While the mission may be similar -- finding and capturing bad guys -- the method will be much different. 
 
 As a HERO trainee, Block will be in a support role, mostly analyzing computer files. It's a far cry from his last, as a soldier in the 3rd Battalion, 75th Ranger Regiment, serving in Afghanistan. 
 
 Block says: "I wanted to be a Ranger my entire life because it's the greatest job you could ever hold. I mean they literally paid you to carry a gun, jump out of an airplane and just be awesome in general." 
 
 But defending your country doesn't come without its share of danger. Sgt. Block's life changed on October 6, 2013, when he and fellow Rangers embarked on a direct-action raid to root out insurgent bombing attacks. 
 
 Block spotted a couple in a courtyard and ordered the two to put their hands in the air. That's when one of the insurgents detonated an explosive strapped to her body. 
 
 He says: "From what I'm told the explosion leveled some of the house. The only thing that separated me [from the suicide bomber] was the guy I was holding onto. And all of his bones ended up in my American flag that was wrapped around my plates and melted. And I think I got a chunk of him in my cheek, because I have shrapnel lodged in there." 
 
 In 2014, Block was named the Army Times' "Soldier of the Year" for courage displayed on the battlefield and his ability to inspire and motivate other soldiers during his rehabilitation. 
 
 But like so many who return home, Block struggled to find a purpose and mission once his military career came to a close. 
 
 That's what brought him to his classroom in Florida, and the HERO Corps which offers a new path to doing what he does best. 
 
 "It's an opportunity for me to go after bad guys again. The complete scope of the crime is a lot more than people probably think," he says. 
 
 And while doctors managed to save the vision in Block's left eye, look at his right eye and you will see something unusual -- a prosthetic bearing the Captain America shield. Sgt. Block is turning his setback into a statement. 
 
 Block says: "He doesn't like bullies. And neither do I." 
 
 Having vision in only one eye, makes staring at a computer screen all day challenging. But Block imagines one day pointing out the shield, to comfort a frightened child who he and a team of law enforcement officers have just rescued from an abusive situation. 
 
 "I'll be honest, looking in the mirror can be tough sometimes," says Block. "But you keep your faith, you keep your confidence, and you go out there and try to make somebody else's life better. It's what you do after-the-fact, and I think I'm trying to do a pretty damn good job." ||||| Hundreds of Thousands of Known Child Pornography Possessors are at Large 
 
 Each of the indicators below represents just one portion of total child pornography trafficking. Based on these indicators, a safe and conservative estimate would place the number of U.S. individuals actively engaged in child pornography trafficking in the hundreds of thousands. 
 
 Key Indicators 
 
 2008: 20,000 Child Pornography Traffickers Identified Daily 
 
 In 2008, the Department of Justice-sponsored ICAC Task Force network, searched the Internet daily for suspects distributing child pornography. This investigation searched only certain types of trafficking in limited areas of the Internet. It also focused on the most graphic and brutal child pornography. In late 2008, this system was identifying 20,000 unique IP addresses daily. Law enforcement has conducted real-time demonstrations of this program for Congress, allowing lawmakers to see thousands of individuals in the act of advertising, trading and distributing movies and images of child sexual abuse. Source: Wyoming Internet Crimes Against Children Task Force. 
 
 2008: 50,000 Child Pornography Traffickers Identified Monthly 
 
 In 2008, The ICAC Task force network was identifying over 50,000 unique computers (as opposed to a larger number of IP addresses) engaged in trading and distributing child pornography on the Internet. Investigators reported that the number of suspects they see was proportional to the number of agents conducting online searches (a number that remains low), as well as the number of known movies and images they track (a number that is also kept low). Source: Testimony of Wyoming Special Agent Flint Waters before the U.S. House Judiciary Committee, 2007. 
 
 300,000 Child Pornography Traffickers Identified Annually 
 
 In 2008, The ICAC Task Force network identified over 300,000 unique computers (as opposed to IP addresses) engaged in trafficking child pornography. There were no reliable estimates on how many suspects use more than one computer to distribute child pornography, though this factor must be weighed against the large percentage of traffic not being monitored by ICACs and the movies and images not identified and searched for by law enforcement. The ICACs have identified millions of crimes and logged over a million potential suspects since 2005. Source: U.S. Senate Judiciary Committee, Subcommittee on Crime and Drugs, 2008. 
 
 "Hundreds of Thousands" of Individuals in the U.S. 
 
 In May, 2006, Justice Department officials were questioned aggressively by Rep. Joe Barton (TX) on the actual magnitude of child pornography trafficking in the United States. Barton expressed concern that DOJ officials were minimizing the true magnitude of the problem because the President's budget had not requested appropriate funding from Congress to deal with the crisis. In testimony before the U.S. House Energy and Commerce Committee, Alice S. Fisher, Assistant Attorney General told Barton that there were "hundreds of thousands" of individuals in the U.S. committing child pornography crimes. (May 3, 2006) 
 
 "Hundreds of Thousands" of Victims of Child Pornography Offenders in the U.S. 
 
 Also under questioning by Rep. Barton, FBI Cyber Division Chief Raul Roldan estimated "hundreds of thousands" of child sexual assault victims of individuals who are also engaged in child pornography crimes. It should be noted that these victims are not necessarily victims of child pornography, per se, but of criminals who are involved in child pornography crimes. Source: Congressional testimony of Raul Roldan, FBI Cyber Division Section Chief, before the U.S. House Energy and Commerce Committee (May 3, 2006). 
 
 Hundreds of Thousands of Victims, Using Extrapolation 
 
 UNH-NCMEC Study: The most well-known study on the link between child pornography possession and sexual assault is "Child Pornography Investigators Arrested in Internet-Related Crimes," conducted by the University of New Hampshire's Crimes Against Children Research Center for the National Center for Missing and Exploited Children. Researchers interviewed law enforcement to determine how often individuals arrested for possession were identified as "dual offenders." The study found that 40% of possessors had sexually assaulted children directly, and an additional 15% were known to have attempted to entice children over the Internet, for a total of 55%. 
 
 National Association to Protect Children Estimates: Although it appears likely that the percentage of child pornography offenders who also sexually abuse children directly is higher, National Association to Protect Children uses an estimate of "1 in 3" (33%), simply in the interest of being conservative. Using the most conservative estimates of the number of child pornography offenders at large, the number who are likely to be "hands on" offenders, and the number of victims each offender has, it is reasonable to conclude that there are hundreds of thousands of American children who are victims of criminals who possess or traffic in child pornography. An alternative approach would be to research the percentage of known child sexual abuse offenders who also possess child pornography, almost certainly higher. 
 
 Over 100,000 Child Pornography Websites 
 
 In testimony before the U.S. House Energy and Commerce Committee, Arnold Bell, then FBI Innocent Images Unit Chief, estimated there are 130,000 child pornography websites. 
 
 Child pornography investigations by federal law enforcement agencies are largely focused on "enterprise" investigations involving organized and commercial child exploitation, rather than wide-scale investigations that might reveal a larger picture of child pornography trafficking. It is unclear, though doubtful, whether the FBI, ICE or U.S. Postal Inspection Service have a technical capacity, similar to Operation Fairplay, to detect child pornography trafficking on a mass scale and thus develop broad strategies for responding beyond their daily triaging of cases. Nor have the federal agencies shown a willingness to be candid about the full magnitude of the crisis, preferring to emphasize their arrests, prosecutions and percentage increase in cases worked, however small. 
 
 Millions of Known Movies and Images 
 
 The National Center for Missing and Exploited Children (NCMEC), a nonprofit agency authorized by Congress to house child pornography, reported in 2007 it had identified 9.6 million images and movies of child pornography. NCMEC reports that just 1,200 victims have been identified from this mountain of evidence. Of these, "35 percent of the photos were taken by a parent, 15 percent by another family member, and 20 percent by someone close to the child or the family." Source: "NCMEC Commentary," Christian Science Monitor (Nov. 26, 2007).
– A group of elite warriors pulled off the battlefield by injury or illness has a new mission here in the US: helping law enforcement take down people who possess and produce child pornography. The HERO Corps (Human Exploitation Rescue Operative) trains veterans in computer forensics, CNN reports. Participants then work as computer forensic analysts, scanning the computers and external hard drives of child pornography suspects. "It's an opportunity for me to go after bad guys again," says former Army Ranger Sgt. Tom Block, who is among a recent class of 24 veterans who will undertake 11 weeks of training followed by 10 months of on-the-ground experience as part of a yearlong unpaid internship. Conceived in 2009 by nonprofit Protect (National Association to Protect Children), the HERO program partners with Homeland Security and the US Special Operations Command. Participants "are truly individuals who have lost their mission on the battlefield," Protect CEO J. Christian tells CNN. For them, the HERO Corps is an "opportunity step back into that role," says Christian, a former Army Ranger who fractured his spine during a mission in Afghanistan. The stats are troubling: Christian says the US leads the world in producing child pornography. In 2008, a study found, more than 300,000 individual computers were being used to traffic child pornography. And a study by the University of New Hampshire found that more than half of people who possess or trade child pornography are "hands-on offenders." That's why veterans like Block want to be HEROs. "Hopefully I can get to them before they get to another child," he says. Injured by a suicide bomber in Afghanistan in 2013, Block wears a prosthetic eye that bears the shield of Captain America. "He doesn't like bullies," Block says of the super hero. "And neither do I."