A spokesman said the defence department takes such matters seriously but would not comment on specific cases.
The Pentagon concern is not just that crimes have been committed, though that alone would be grounds for dismissal, but that it makes those involved security risks.
One of those charged was a contractor who had security clearance at the National Security Agency, which eavesdrops on communications worldwide. He fled the US and is thought to be hiding in Libya.
Details about links between the Pentagon and child pornography were disclosed yesterday in the Boston Globe.
The paper quotes an internal report from the defence criminal investigative service in 2009 which says that though the number found to be involved is small compared with the number employed by the defence department and related organisations, it leaves those involved "at risk of blackmail, bribery, and threats, especially since these individuals typically have access to military installations".
Some of the pornography was downloaded on government computers.
The Globe obtained 50 pages of documents relating to an investigation by the inspector-general of the Pentagon that had not been made public. At least 30 cases have been investigated.
One case involved a national security official who possessed 8,400 pictures and 200 films and was sentenced to five years in prison.
Many others have also been sentenced and more people are still under investigation.
Another individual alleged to have been involved was working at the national reconnaissance office in Virginia, which operates the military's spy satellites. He was not charged but sent to a lower level job in a field office in New Mexico.
Some of the cases came to light as a result of an investigation by the immigration and customs agency, whose Operation Flicker in 2006 identified 5,000 people who had paid for access to overseas pornography websites.
Among the 5,000 were a contractor at a weapons-testing base in California and another at a naval air warfare centre in the same state.
Illustrating the problems of bringing cases to court, a manager at an advanced secret weapons centre was found to have images on his computer that appeared pornographic -- but it could not be established that the children had been abused.
A worker at a separate establishment also had pornographic images but the ages of those involved could not be determined and so it could not be established they were children.