- "That puts the epicenter of the seven point one earthquake right in the heart of the San Francisco Bay. We've also been getting strange reports of something moving under the Golden Gate Bridge."
- —Unidentified news reporter.
K-DAY is the given name for the first Kaiju attack on humanity. The incident took place on August 10, 2013 through August 15, 2013 in the cities of San Francisco, Sacramento, and Oakland. K-DAY marked the beginning of the Kaiju War.
Prior to the creature's appearance, an earthquake measuring 7.1 on the Richter Scale was recorded. The epicenter of the quake was in the middle of the San Francisco Bay. It may be logically speculated that this quake was in fact the footfalls of the Kaiju as it walked on the relatively shallow floor of the bay after swimming in from deeper water.
The creature emerged out of the waters of San Francisco Bay and destroyed the Golden Gate Bridge, killing hundreds of motorists as their vehicles plunged into the bay amid falling steel and concrete from the destroyed bridge.
News reports of the quake were quickly followed by “strange reports of something moving under the Golden Gate Bridge”. Video footage of the Kaiju attacking the bridge was broadcast by news organizations all over the world. Reporters estimated the beast to be 300 feet tall. Successive news reports showed the devastation it inflicted on San Francisco and the surrounding cities, and the futile attempts of the combined forces of the US and United Kingdom military's ground forces and airstrikes to kill it.
The creature then went on a 35 mile rampage along the American Pacific coast, devastating the cities of Sacramento and Oakland over the next six days. The United States and British militaries responded to the giant creature, fighting it over the course of the six days. With troops, tanks, heavy artillery and jets attempting to kill the creature, they were unable to succeed in stopping it.
On August 15th, the military finally resorted to using tactical nuclear missiles to kill the creature, in which they succeeded. It took three such missiles to bring the beast down, and the nuclear fallout and Kaiju blood left large swaths of the Bay area uninhabitable for centuries. The San Francisco Bay Area area was later named the San Francisco Exclusion Zone, or SFEZ.
Tens of thousands of people were killed throughout the beast’s rampage. Noted fatalities include UK Royal Air Force officer Luna Pentecost, sister of the fellow RAF pilot, Stacker Pentecost and Yeye Choi, grandfather of Tendo Choi.
Humanity was stunned by the devastating attack. The people of the devastated cities "mourned their dead, memorialized the event and moved on."
The creature's attack marked the beginning of incessant attacks by Kaiju against large areas of Human population centers. K-DAY was the start of a war that would last for another twelve years.
The creature was later designated "Trespasser" by the Pan Pacific Defense Corps after the organization was formed. Later, the Jaeger Program was founded to create a weapon strong enough to combat the Kaiju.
- According to the prologue of Pacific Rim, Trespasser's attack destroyed the cities of San Francisco, Sacramento and Oakland. However, Travis Beacham states that Trespasser attacked San Francisco, Hayward, San Mateo and San Jose.
- The F-22s depicted attacking Trespasser bear the "FF" tail codes of aircraft based at Andrews Air Force Base, as part of the 1ST Fighter Wing, outside Washington, D.C.. Although fast, the F-22s would not have been able to respond that fast. The film's intention likely may have been to use fighter aircraft bearing the code "WA" of the 57TH Wing of Nellis Air Force Base, in Las Vegas, Nevada, or the "ED" code of the 411TH Flight Test Squadron at the Edwards Air Force Base.
- Other military aircraft shown in the opening montage include CH-47 Chinooks and FA-18 Hornets.
- In Tales From Year Zero, other aircraft seemingly present include AC-130U "Spooky" gunships and the F-35 Lightning II. The latter of these would not have been operational at that time, but some would have been nearby at Edwards Air Force Base as part of the international testing and development efforts for the aircraft.
- Its name may be a reference to the D-Day, an oceanic invasion which occurred June 1994 during World War II.
Tales From Year Zero