Three controversial anti-riot vehicles armed with water cannons will hit the streets of Hong Kong this week ... since been stationed at the Police Tactical Unit headquarters in Fanling for training.

The Special Duties Unit (SDU) is an elite paramilitary tactical unit of the Hong Kong Police Force and is considered one of the world's finest in its role. But being the best carries its own burdens.

Hundreds of Hong Kong police officers are on the lookout ... The force’s counterterrorism response unit, police tactical unit and an anti-riot “Sabre-toothed Tiger” vehicle were deployed ...