Some 3,000 troops backed by helicopters and armored vehicles occupied the Rio slum on Sunday without firing a shot, in the latest effort to improve security and end the control of drug gangs over the city, Reuters reported. Brazilian security forces have taken over about 20 slums over the past three years but none is as important as Rocinha, a sprawling area full of shacks situated between the main city and western areas. Police squads patrolled the narrow streets of Rocinha and snipers took positions on rooftops as tanks rolled through the alleys and helicopters flew overhead. The occupation of the slum ended without any serious incident. According to police officials, the preparations to attack Rocinha involved months of planning. Dozens of reporters followed police and soldiers up through empty, garbage-strewn narrow streets. Most of the gangsters and even common people fled the area as authorities announced their plans days in advance. Only one person was reported arrested during the whole operation and troops later raised the Brazilian flag over the territory to show Rocinha's "return" to the state.