(Capcom's primary storyline)
The 1st Special Forces Operational Detachment-Delta (1st SFOD-D), popularly known as Delta Force, is a U.S. Army unit used for hostage rescue and counterterrorism, as well as direct action and reconnaissance against high-value targets.
Delta Force was established in the 1970s when the operations of the British Special Air Service indicated an increasing trend in unconventional warfare.
Raccoon City mission
In 1998, a feud erupted between the US military and the Umbrella Corporation over the G-Virus. Dr. William Birkin, its developer, sought to hand it over to the military in exchange for asylum. Highly prized by both parties for its promise in bio-weapons development, the Umbrella Security Service's botched G-Virus Seizure Operation led to the t-Virus enveloping Raccoon City. With Congress discussing the option of bombing the city as an effective means of containment, a Delta Force team was quickly sent in late on September 28 to apprehend it. As a trump card, they were entrusted with an experimental rail cannon, the Demon Sword of Paracelsus.
Thanks to a number of moles the US government had within Umbrella U.S.A., it was understood that Dr. Birkin's facility was located somewhere in the industrial zone to the north-east. However thanks to counterespionage by Umbrella's own moles, the correct location was not provided. Instead, the Delta Force team was sent to a scrap yard outside Umbrella's Incineration Disposal Plant P-12A. Aware of the intrusion, Umbrella's paramilitary leader for city operations Colonel Sergei Vladimir gave the order for five T-103s to be dropped at the yard to ambush and destroy the team, either unwilling or unable to provide a USS team. Delta Force succeeded in destroying them with the help of the experimental anti-B.O.W. weapon, Demon Sword of Paracelsus, but at the cost of the entire unit in the early hours of September 29. Former soldier Jill Valentine, who was given the honour of training alongside Delta Force in bomb disposal, escaped from the city via the scrap yard and saw their bodies.
Consequences of Raccoon City
Following Delta Team's loss, the US military began establishing new units trained in Anti-B.O.W. combat. USSTRATCOM's Anti-Umbrella Pursuit and Investigation Team was established immediately after the city's destruction, and was tasked with covert operations. The more conventional and larger Federal Bioterrorism Commission, was established to tackle B.O.W.s in a more conventional manner.