The battle for the capture of Yokohama Hive (also known as Operation Lucifer) took place from August 5th to August 9th, 1999. It was the first offensive operation against the BETA in the Far East Defence Line, with participation by the Imperial Japanese Army/Mainland Defence Force, the United Nations Force (heavily dominated by United States troops during the final stages, despite their withdrawal from the security treaty with Japan one year prior), and COSEAN military forces.
After the establishment of a Hive on Sadogashima Island and the assault on Kyoto, the invasion of the BETA slowed, and the Japanese government and seat of power was relocated to Tokyo where the defence line was solidified against the BETA advance. However, when news of the construction of the Yokohama Hive began, the Japanese government and the Imperial Army, already barely holding up against the BETA from the Sadogashima Hive, realized that a Hive situated on the mainland would end the Empire of Japan entirely.
The United Nations also considered the possibility of losing an important component of the Far East Defence Line, and proposed a plan to attack the Yokohama Hive. The Imperial Army agreed with the proposal, and Operation Lucifer—the largest human offensive since Operation Palaiologos—was set into motion. The operation aimed to complete two objectives; an all-out assault and infiltration of Hive 22 for its eventual capture, and the reclamation of the Japanese mainland from the BETA. On the 5th of August, the IJA/MDF and allied forces launched their assault from both the Pacific Ocean and Sea of Japan, maneuvering to encircle the Yokohama Hive.
The forces of the Far East Defence Line made infiltrating the structure and securing its interior their primary goal, despite the shock of having discovered that the Yokohama Hive's reactor had grown from Phase 2 to Phase 4 within a year. This was important to orbital forces, as a Phase 4 Hive meant the appearance of Laser-class BETA on the field, severely curtailing their plans for this operation.
The United Nation's Special Task Force A-01's 7th Squadron Dellingr was also deployed as combat observers during the main phase of Hive assault, with the eventual goal of securing the Hive Reactor. After witnessing a TSF infiltration force getting encircled by BETA however, 2nd Lieutenants Narumi Takayuki and Taira Shinji of the 7th Squadron overrode their standing orders and entered combat, drawing off a majority of the BETA from the force.
Halfway through the battle, the overall combat plan was interrupted by the United Nations Space Command, which warned all troops to evacuate the area in preparation for a massive wide-area attack. This was the prelude to the first usage of a G-Bomb in human history, and despite the scant time given, two G-bombs were dropped on the Hive. The first blast was at 08:15 on the 6th of August and destroyed a portion of the Hive monument, and a second blast that soon followed cleared most of the Hive's upper layers.
Immediately following this, BETA groups in western Japan began withdrawing for the continent, suffering great damage from pursuit and bombardment attacks. Troops that followed in the wake of the G-bomb blasts managed to secure the Hive structure by clearing BETA from the tunnels. Coupled with sudden mass inactivity of BETA groups underground, the Yokohama Hive Battle ended in humanity's victory; the first of its kind since two and a half decades of defeats.
Despite the success of Operation Lucifer, the victory served as a wake-up call to many and ultimately soured relations between the world and the US military, and with Japan in particular. The insistence of US/UN command to deploy the G-Bomb despite resistance from the Japanese government, lack of time for evacuation given to friendly troops that were still entangled in combat resulting in needless deaths, as well as the usage of an untested weapon on mainland Japan angered the Japanese government greatly, especially after the battle when time was devoted to the study of the G-bomb's blast power and effects on the land.
More galling to them, however, was the US statement issued soon after that suggested that the only surefire way to take a Hive would be to rely on a G-bomb centered strategy, and renewed political conflicts regarding the distribution of the G-Elements in the Yokohama Hive. This event would later be an indirect trigger for the 12/5 Incident led by Sagiri Naoya, as he was present at the battle, and having witnessed the destructive power of the G-Bomb first-hand, felt even greater hatred towards the Japanese government for not forcing the bombing to be called off.
The new G-bomb centric policy also heavily affected decision-making processes in the US' Advanced Tactical Surface Fighter program due to the cancellation of the Hi-MAERF Project, and resulted in budget cuts to the development programs of both the YF-22 and YF-23.
The greatest act of damnation, however, was the daring strategy of keeping the Hive reactor alive for research purposes, and Yokohama Base was re-established to cover the area on top of the reactor. This would not only attract the attention of groups opposed to the usage of BETA-derived technology and compromise security of the Yokohama Base, but would also result in the Defence of Yokohama Base battle that would nearly destroy humanity's last chance at victory. The decision was sound, however; the Yokohama Hive's progression to Phase 4 in such a short amount of time was seen as unnatural despite the Hive structure retaining Phase 2 characteristics, and the various never-before-seen evidences of BETA behavior found within the Hive would prove to be a potential gold mine of information about mankind's enemies.
Another less-known aftermath of the G-Bombs usage was the creation of a Causality Conductor.