The Kempeitai was the military police of the Imperial Japanese Army. The organization also shared civilian secret police, espionage, and counter-intelligence roles within Japan and its occupied territories, and was notorious for its brutality and role in suppressing dissent. The broad duties of the Kempeitai included maintaining military discipline, enforcing conscription laws, protecting vital military zones, and investigating crimes among soldiers. In occupied areas, it also issued travel permits, recruited labor, arrested resistance, requisitioned food and supplies, spread propaganda, and suppressed anti-Japanese sentiment. At its peak at the end of World War II, the Kempeitai was an extensive corps with about 35,000 personnel.

Waterboarding is a form of torture in which water is poured over a cloth covering the face and breathing passages of an immobilized captive, causing the person to experience the sensation of drowning. In the most common method of waterboarding, the captive's face is covered with cloth or some other thin material and immobilized on their back at an incline of 10 to 20 degrees. Torturers pour water onto the face over the breathing passages, causing an almost immediate gag reflex and creating a drowning sensation for the captive. Normally, water is poured intermittently to prevent death; however, if the water is poured uninterruptedly it will lead to death by asphyxia. Waterboarding can cause extreme pain, damage to lungs, brain damage from oxygen deprivation, other physical injuries including broken bones due to struggling against restraints, and lasting psychological damage. Adverse physical effects can last for months, and psychological effects for years. The term "water board torture" appeared in press reports as early as 1976.