Night City Holocaust

The Night City Holocaust, also known as the Arasaka Headquarters Bombing or AHQ Disaster, was a nuclear disaster in Night City that occurred on August 20, 2023.

Detonation
During the Fourth Corporate War, on August 20 2023, a Militech incursion team led by Morgan Blackhand and Johnny Silverhand attempted an infiltration mission into the Arasaka Towers of Night City in order to steal/destroy the Arasaka Corporation's Reliquary Database Project. The idea was to render the project unusable for the rival corporation by using a tactical nuclear device (or "pocket nuke"), with the planned area, a heavily shielded complex, to absorb the impact of the blast and prevent massive destruction. However, due to the firefight between the Militech SpecOps and the Arasaka troops, the nuclear device somehow prematurely detonated on the 120th floor of the southern tower, 366 meters/yards above the ground, inside Kei Arasaka's apartment bunker where the Soulkiller laboratory was located.

The explosion instantly obliterated the Arasaka Towers, splitting them in half and causing both structures to collapse outward. The entire City & Corporate District turned into ruins within seconds, with almost everyone in the immediate area dying. The blast instantly incinerated over 12,000 people in the vicinity of the Towers, and fatally injured upwards of half a million more. Another quarter million died in the resulting aftermath over weeks and months.

As the detonation went off at roughly 366 meters/yards above the sea level, the explosion was technically an air blast, and while this lessened overall long-term radioactivity, most of what remained penetrated only the huge skyscrapers surrounding the blast area. Since much of the metropolis was built on fill, and because the elevation was originally very low, the nuke caused a minor earthquake that liquefied parts of the fill and flooded the inner city. The huge blast turned the tons of raw concrete and steel of the buildings into particulate debris that covered the entirety of Northern California and far out to sea for many months, as well as igniting a fierce firestorm that covered thousands of acres beyond Night City. This combined dust cloud spiraled up into the sky and turned it red with particulate matter for almost two years. And even many years after the explosion, suspended particles caused the skies at dawn and dusk to glow a lurid red, inspiring people who lived through that timespan to call it the Time of the Red.

Aftermath
Night City was barely habitable within 24 hours of the detonation. Lots of Night Citizens were unaffected by the initial fallout as they were mostly cybered up or had radioactivity filters installed in their bodies already. However, the firestorm destroyed a large portion of the city's housing, forcing people to move over to either the suburbs on the other side of the bay, or to areas further out. The liquified shaking soil caused by the explosion broke gas mains, water pipes, and electrical grids.

Then-US President Elizabeth Kress blamed the Night City attack on the Arasaka Corporation. However, she was soon able to determine that the actual weapon used had been supplied by a Militech strike team. The Big Lie pushed forward by Militech and the USA was that Arasaka themselves had blown up the Corporate Center of Night City in an area denial attack to stop Militech from seizing control of the Arasaka Towers. Truth is that it was was never formally decided who had triggered the explosion. In the public's eyes, the reasoning for the nuclear detonation was never uncovered. Some believed it was Militech's overzealous desire to crush Arasaka, while others believed it was an area denial weapon set off to protect the Arasaka Towers.

Within hours of the disaster, President Kress nationalized Militech through the expedience of their CEO, General Donald Lundee, and his reserve commission. Militech was placed thoroughly under the control of the still sizable United States military, and banished all Arasaka forces from the continental United States under the threat of a retaliatory strike on Arasaka's Tokyo headquarters. Other nations swiftly followed the US's lead, nationalizing and/or interdicting assets of both participants of the Fourth Corporate War.

Legacy
During the rebuilding of Night City, much of the radioactive rubble was tossed into Del Coronado Bay, while the ground zero of the nuclear explosion became known as the Hot Zone, an area of Night City filled with the ruins of the disaster. By 2045, much of the radiation had subsided, but it was still present to some level.

During the Time of the Red, a young independent media known as Trace Santiago managed to obtain information about what truly went down in 2023, writing several exposes and books about the Fourth Corporate War and the AHQ Disaster. With this story published in the early 2040s, the Big Lie - the deception created by President Kress and Militech to blame Arasaka for the nuclear detonation - completely crumbled. This publication backfired spectacularly against Militech and the New United States of America, driving Night City to realign itself with Arasaka rather than the NUSA. After these revelations, it was a common opinion that Night Citizens would prefer to see the return of the Asian corporation than submit to federal rule.

In 2077, Hanako Arasaka cited the initial death toll was around four thousand Arasaka employees and Night Citizens.

Arasaka Nuclear Device
The bomb that destroyed the Arasaka Towers was from Militech, but Arasaka had a much more powerful thermonuclear device hidden beneath the building's foundation at the time of the explosion. According to Michiko Arasaka, this nuke was planted in the Towers in case Militech managed to overrun its defenses and take possession of the secrets hidden within. Only a handful of people at the top of the corporation knew about it, such as its current CEO at the time, Kei Arasaka, and his father Saburo.

Shortly after the incident, Kei sent people to find if the bomb that had detonated was theirs, eventually finding out it had been a Militech device instead. They searched for their device but to no avail. Concluding that only someone very strong could have taken it, the search team used radiation scanners and found a trail that led outside of the Hot Zone and to the garage of a borg by the name of Samantha Stevens. While the team was searching for the bomb, Kei Arasaka was killed, and the search team was left without instructions on how to proceed. Ultimately, it was decided to simply leave the device where it was, but keeping a close watch on Samantha and the garage until the bomb was moved. In truth, Samantha had accessed the Hot Zone to explore a wrecked bunker in the Towers' ruins, only to find out the lifeless body of Johnny Silverhand and an undetonated nuclear device. She tossed its contents into Del Coronado Bay, and used the bomb's crate to hide Silverhand's body.

Fifteen years later, Michiko Arasaka followed the group that was tasked with moving the crate to New Mexico, where she intercepted them and told the truth about the device. Knowing how dangerous it would be if any of the factions within Arasaka got their hands on it, she decided to help the group reach Los Alamos Labs to safely dismantle it, not knowing the crate didn't contain the bomb.

Apart from Samantha Stevens, Angel is the only other person that knows where the device's contents are located. It's unknown if by 2077 someone has retrieved it, or if it's still in Del Coronado.

Development
Mike Pondsmith commented about the nuke on Reddit:
 * Ah, The Nuke. I spent way too much time with fallout and destruction tables to make sure this worked. To save making you guys read all that (40+ pages), I'll sum up. The suitcase nuke was based on a prospective terrorist bomb concept, which was about .5Kt. I used San Francisco as the target model, siting the blast at about Coit Tower. It went off halfway up the Tower, which absorbed the blast and put it around 1200 feet up. The Towers were surrounded by equally huge and tall structures that absorbed much of the initial shock wave (and fell outwards, causing much of the secondary destruction, but limiting the scale of impact). The Nuke was a "clean" device, so radioactive fallout was minimized (the point was to wreck the Arasaka database, not the City). About 15K were instantly killed in the blast, with upwards of 100K dying over time from aftereffects like radiation, firestorms, building collapse... As I was doing this research and using fun tools like Alex Wellerstein's Nuke Map site (https://nuclearsecrecy.com/nukemap/), I seriously expected the feds to kick in RTG's doors and arrest the lot of us.
 * Yeah, I did way too much research, but the topic fascinated me. For most of my life, I lived with the idea that WWIII would wipe humanity out (clock is still ticking, BTW). The NC Nuke was me working out exactly how bad a nuke really can be. I also wanted to show that almost any Corp could have gotten a nuke--it was symptomatic that both of these guys, born out of a WWII background, could seriously consider atomic weapons as an option. There is an entire short story I wrote that happens at Ground Zero that day, and how Samantha (the full conversion firefighter) ended up with Johnny's body. I was planning to put it into Aftershocks, but the day I finished the story--in fact, about 20 minutes after I finished--somebody flew a plane into the last of the Twin Towers (I had CNN on) and suddenly it was no longer appropriate to release it in the face of so much real world death.

Trivia

 * The power of the AHQ Disaster bomb was about a tiny fraction of the Hiroshima bomb.
 * The explosion was technically an air blast, as the detonation went off at roughly 366m/yds. Little Boy, in comparison, had a detonation height of about 579m/yds.
 * The nuclear device was basically a tactical nuke not much larger than a suitcase bomb. Similar to a 1950s Davy Crockett backpack nuke, with an overall yield of .1 kiloton.