The Kempeitai (Japanese, 憲兵隊) was the military police arm of the Imperial Japanese Army from 1881 to 1945. They were infamously brutal throughout the empire Japan built in that period, known for warrantless arrests, torture, and execution of prisoners. During World War II their notoriety reached its greatest heights as the Kempeitai ran forced labor camps in Southeast Asia performed mass executions of Allied prisoners (leading to many war crimes trials after V-J Day). At this time they also became feared in Japan itself, as Prime Minister Hideki Tojo used them in the capacity as a secret police force to coerce support for his government's policies.
The handling of civilians in Hawaii earned the Kempeitai more ill repute. For example, a half-Hawaiian local named Charlie Kaapu was arrested by the Kempeitai purely on the say-so of a Japanese major whom Kaapu had cuckolded.