Armored cars rolled through smoke-filled streets in Rio de Janeiro on Thursday as police battled slum-based drug gangs for a fifth consecutive day in the city slated to host the 2016 Olympics. Live TV coverage showed heavily armed police exchanging gunfire with suspected drug traffickers in the hilly shantytowns on the city outskirts. Police targeted the Vila Cruzeiro slum in the northern part of the city, considered a stronghold of a gang thought to be behind ordering attacks. At least 10 armored Marine vehicles, never before used in battles in the city's slums, or favelas, transported soldiers into Vila Cruzeiro,...