People in the armed forces were quick to catch on to the Internet. After all, the Internet was created with Department of Defense money. But it was at the troop level that things got really interesting. The U.S. military is spread all over the planet, and troops are always eager to get an idea of what its like in various places they might end up. This includes not only actual places, but units and ships. This curiosity has reached life-and-death proportions when it comes to going to Iraq or Afghanistan. So as soon as the soldiers find out they are headed overseas to replace a particular unit, they get in touch with people they are going to replace. And they talk shop.
This is all unofficial communication, and it makes the security people nervous. The troops generally use non-military email accounts. Its an open secret that .mil email accounts gets run through a security filter before anything is delivered. While the troops are aware of the importance of OPSEC (operational security, what they do, how they do it and so on), these emails often get into more detail then they ought to. Normally, this is not a problem. For all the talk of how unsecure email is, the vulnerability is more theoretical than practical. Where there have been obvious problems is on public bulletin boards and chat rooms. There have been a few incidents of troops unthinkingly revealing dangerous information, usually about tactics, security at bases or intelligence matters. The few times this has been found out by commanders, nastygrams were sent to the offenders commanding officer. Apparently there have been no court martials over this so far. After all, the troops are acting in good faith, and most of the communication remains via email. Troops are warned to stay out of public venues with these discussions. And the discussions are is getting results. Soldiers and marines arrive with detailed knowledge of what they are getting into. Security and intelligence officers arrive with an ulcer.
The rotation of new units to Iraq and Afghanistan has resulted in a not-unexpected development. The replacement troops get in touch, informally, via the Internet, with the people already there and discuss details of what the new guys can expect. Now this sort of thing has gone on, at a much slower pace, since World War II. Until the Internet came along, the units waiting to go overseas, would either send some people ahead to get an idea of what to expect, or some people already over there would come back and provide details. There were also various reports sent back from the front. Mostly general stuff, somewhat useful. But its all changed now.