Biological warfare

Biological warfare, also known as germ warfare, was a form of warfare which utilised harmful bacteria or diseases as weapons.

The Fourth Doctor observed "most warfare is biological. In the sense that living things tend to be involved on one level or another." The standard definition, however, generally specified the use of viral agents or biological weapons during conflict. (PROSE: Drift)

Examples
Following the Japanese invasion of Manchuria, the military scientist Ishii Shiro led efforts to develop biological weapons. The Japanese infected Chinese prisoners with bubonic plague to observe the effects on the human body. Sponsored by the Japanese Emperor himself, the experiments were performed in Zhong Ma Fortress and its successor, Unit 731, which produced germ-ridden packages which were dropped on Manchurian and Chinese villages until throughout the Pacific War. After the war, many of the perpetrators were never brought to justice and the United States even used the data to deploy biological weapons against North Korea during the Korean War. (PROSE: Log 384)

During the Second World War in Europe, the British organised the covert Operation Shaker in preparation for a German invasion. The South Mendip Auxiliary Corps, who were not made party to the involvement of the Shakers or their abilities, the Mendips simply heard that they should expect clusters of occupying Germans to die of apparently-natural causes. Concerned that this involved the use of some type of gas, they raised their concerns with their superiors about the use of germ warfare. Because of this misunderstanding, they were told little more about the operation in order to keep it a secret. (PROSE: Losing the Audience)

The Daleks utilised biological warfare during the Dalek Wars. On the eve of the Second Dalek War, they attempted to create a virus on Spiridon, but it was released prematurely and they were later forced to destroy the facility. (TV: Planet of the Daleks) During the Third Dalek War, they unleashed space plague on the Outer Worlds, resulting in the Exxilon Gambit to secure the only known cure, parrinium. (PROSE: The Secret Lives of Monsters, TV: Death to the Daleks) Later on, they became a victim of biological warfare themselves when the Movellans created the Movellan virus, (TV: Resurrection of the Daleks) which caught the Dalek Empire totally unprepared and had devastating results. (PROSE: Remembrance of the Daleks)