The Battle of Kalm is an armed engagement in Dirge of Cerberus -Final Fantasy VII- between the Deepground and the World Regenesis Organization, and marked the start of the Deepground War. The Deepground take the WRO by surprise with a massive airborne assault on the city, but are ultimately repelled with the help of Vincent Valentine.
Background and goals
The Deepground has existed in secrecy for years, and consists of an elite battalion of SOLDIER that was trapped under the ruins of Midgar for three years. Emerging for the first time, they seek to capture as many people who are not infected by Geostigma, Jenova cells or other contaminants as possible. For reasons at that time unknown, they also specifically target Vincent during the attack; it is later revealed that this is because he holds the Protomateria needed to control Chaos, the messenger that is required to awaken Omega, the final and Weapon.
The Deepground attacks in the evening when the people of Kalm are celebrating the recovery from Meteorfall. Due to the element of surprise, the Deepground fighters are able to capture a large number of civilians before the WRO is able to react. Vincent reluctantly becomes involved in the fighting and defeats Dragonfly in the first boss battle of the game. In a later conversation with Reeve Tuesti, Vincent agrees to assist the WRO and fights the Dragonfly again, now in the form of Dragonfly GL. Vincent destroys Dragonfly once and for all, while the WRO eventually succeeds in regaining control of the city.
To the WRO, the victory is short-lived. An attack on Edge is reported almost immediately after the battle is over, and the organization is forces to mobilize as the mysteries surrounding Deepground remain as unclear as ever. The Deepground also attacks Junon and Wutai (as briefly mentioned by Yuffie Kisaragi), and the war eventually culminated with the Battle of Midgar in which the WRO goes for the hornet's nest.