In the early hours of May 16, 2010, half a dozen heavily-armed police officers from the Special Response Team, the city's SWAT unit, stood outside of a duplex in Detroit, ready to enter the house of a murder suspect.

The policemen threw a flash-bang grenade through one of the house's windows. The grenade landed so close to the room's bed it burned its blanket. An officer burst through the bedroom's window and fired a single shot, killing 7-year-old Aiyana Stanley-Jones.

The incident could be seen a tragic example of a SWAT raid gone awfully wrong. But the American Civil Liberties Union (ACLU) thinks that raids like the one that ended Stanley-Jones' young life are representative of a worrisome trend: the unchecked militarization of police departments across the United States.

In an unprecedented report, the ACLU exposes how much local police departments rely on SWAT raids for routine operations, using military gear. Military equipment - sometimes already used in battle overseas - can be obtained for free by police departments thanks to a Department of Defense program.

"The police in America has become too militarized," Kara Dansky, the ACLU Senior Counsel, and main author of the report, told Mashable. "This has the effect of terrifying people, destroying communities and actually undermining public safety."

The vast majority (80%) of more than 800 SWAT operations carried out by 20 police departments during 2011-2012 resulted from simple search warrants, most of them drug-related, the report said. The SWAT team was deployed for hostage crises, shootings or other dangerous situations in only 7% of the total operations.

Image: ACLU

The ACLU obtained most of its data used for the report by submitting public information requests to more than 260 police departments in 26 states, producing 3,844 records — "a snapshot of the militarization of police," as the ACLU report puts it. What are the causes of this increased militarization? Police first began stockpiling heavy-weaponry and military-grade gear for the war on drugs, the report said. The federal program encouraging police departments to acquire the used military equipment has helped fuel this militarization.

Since 2006, police departments around the country have collected almost 500 mine-resistant armored vehicles (also knowns as MRAPs), almost 94,000 machine guns, and more than 500 planes and helicopters, according to a recent New York Times investigation.

Often, the equipment is unused but on occasion police have abused the weapons, as Wired reported in 2012.

To justify the acquisition of heavy weaponry, police officers often cite 'terrorism' in their requests for grants.

"Our application talked about the danger of domestic terrorism, but that’s just something you put in the grant application to get the money," a Keene City council-member said, according to the ACLU. "What red-blooded American cop isn’t going to be excited about getting a toy like this?"

To slow down this "dangerous" trend, the ACLU offers a series of proposals, such as putting cameras on SWAT team members' helmets, passing legislation to limit the acquisition of military-grade equipment, and enacting clear-cut policies for when the use of SWAT teams is appropriate, among others suggestions.

"We want the police to protect and serve our communities, not wage war on the people who live in them," Dansky said. "And when the police treat people in communities like enemies that has the effect of undermining the public confidence in law enforcement."

An excerpt from the report is embedded below. You can read the full report on the ACLU's website.

ACLU Police Militarization Report