The sight of Blackhawk helicopters scouring the skies over Denver on Monday and Tuesday night looked like a scene from a movie. Instead, it was an anti-terror drill that surprised and concerned residents, who had not been warned about the exercise.The choppers came in low, right on top of the buildings in downtown Denver, creating plenty of noise and attracting loads of concerned looks."It looked to me like they were Blackhawks and they were trying to practice dropoffs and pickups," said Baerbel Merrill, who saw the Blackhawks.The drill was a multi-agency operation involving special forces in the military and Denver police."It actually prepares us for the global war on terrorism, to go into an urban environment," said Lt. Steve Ruh, a spokesman for the U.S. Special Operations Command. "It will help us respond better if the need calls for us to come in."The training exercises are not related to any security training for the Democratic National Convention in August, said Lt. Nathan Potter, with Special Operations Command. Although, sources inside the training tell 7News the Democratic National Convention definitely played a role in choosing a site for the operations."There were helicopters but there were no lights. And they were just practicing. They were going in between the buildings and they were very low," said Cindy Rodd, who saw the hovering choppers.There was also activity on the streets of Denver as well. On Tuesday, a special team from the Department of Defense rumbled through downtown, with big sport utility vehicles carrying sophisticated communication equipment that belong to the Weapons of Mass Destruction Civil Support Team, or CST.The CST team, based in Wyoming, is designed to respond immediately to any act of terrorism. Team members would not comment on their mission."Is this a normal occurrence here or is there something funky going on that we should be wondering what we ought to be doing next?" said witness Bill Whitaker.U.S. military Special Operations commandos will continue conducting the counter-terrorism training from early afternoon until 11 p.m. through Friday night, according to the Rocky Mountain News.None of the agencies involved informed the public or news agencies about the drill and that may have had an effect on Denver's 911 system.Denver dispatchers answered at least 140 calls pertaining to the exercise, with calls averaging about 30 seconds. So between 7 p.m. and 11 p.m. Monday there were at least 70 minutes where dispatchers were handling preventable, non-emergency calls, related to the unannounced drill.Denver police gave dispatchers specific language on how to respond to 911 callers. Dispatchers were told to say this was a "Denver SWAT team exercise" although that's not entirely accurate since there was also military involvement.So even though Denver police knew the exercise would lead to calls to emergency dispatchers, they chose not to alert the public.Denver's mayor said it was a misunderstanding."The federal agencies sponsoring the ongoing multi-agency training in Denver agreed to make the proper notifications regarding the exercises to prevent surprise and inconvenience to Denver residents. There seems to have been a misunderstanding about the reach and scope of these notifications, and they did not occur in the manner expected by the city," Mayor Hickenlooper said in a statement."Although these exercises are in no way connected to the upcoming Democratic National Convention, Denver officials were well aware that there would be heightened sensitivity to an exercise such as this because of its proximity to the convention. Denver recognizes that these are our federal partners, and we are fortunate that they have chosen Denver for their training exercises. Should there ever be an emergency here that would require federal assistance, they will be familiar with our city and how best to navigate it."