It was in 2009 that the portal opened. There was no real warning; if there had been something that set it off, some accident or event somewhere in Tokyo in a lab, or some strange convergence, then all evidence in gone now.
Square miles of city were annihilated in moments as ‘the event’ swallowed them up. It looked like a gas giant planet, embedded in the ground and gouging a chunk out of Japan. It was visible from miles away, deforming the horizon and visible from space. It tore up the ground, and the devastation ruined the land around it for miles.
And that was all after-effects. What happened at the time was what everyone remembers. They came, the invaders. Swarms of their fighters, bombers, transports and other craft swept through the barrier, opening fire on refugees, intact buildings and facilities, military assistance and more. Spreading outward, they landed ground troops and began to pillage and plunder everything. Prisoners were taken, materials were looted, and more destruction followed. More and more of them followed, and in turn the forces of Earth began their counterattack.
After 5 years of brutal fighting eventually, we learned more about them, through knowledge from their original captives. Bought with them as slaves and 'resources', after a daring and near-suicidal attack on one of the Yerrill hives after months of planning, work, and dedication, the fortress was taken.
Inside, human forces found the first of their Avalonian allies. Once captives of the Yerrill, they had fought them for nearly two decades themselves, working as a resistance movement and fighting as guerrillas. The Avalonians turned over their knowledge of the Yerrill, giving humanity the information it needed to counter their communications and jamming, to disrupt their logistics, and to begin to fight back in a concerted effort.
The next series of attacks swung into action, and slowly but surely the Yerrill were forced back. Over the next 18 months, they pushed the aliens back, finally culminating in the Battle of Tokyo, a massive aerial, naval and ground amphibious attack that devastated the last pair of Yerrill hives and eradicated their forces on Earth, driving the last of them through the portal.
The portal - by now named ‘Tokyo Jupiter’, because of its’ appearance - was ringed by defences, outside of an exclusion zone of fifty miles.
And then humanity caught its breath.
The portal still remained, which meant that another ‘event’ could happen anytime soon. And there was the question of what was on the other side. The decision was almost unanimous, though it came after another two years of discussion and debate. And there was also the question of the Avalonians, humanities' new allies and still imprisoned on the other side of the portal and under the occupation of the Yerrill.
It had to be explored, the war had to be taken to them.
Drones and probes were sent through to chart the world on the other side, and extensive interviews and intelligence gathering sessions were undertaken with the Avalonians, charting and mapping the world on the other side of the portal. Knowledge of its' many dangerous life forms, and of the Yerrill's forces was gathered - at least until the drones and probes were destroyed, either by the Yerrill or the hostile wildlife or conditions on the planet itself.
A special committee of the UN was formed, one with primarily military goals in mind: it’s job would be to establish an operating base on the world beyond Tokyo Jupiter, and bring the fight to aliens. The species they held enslaved on the other side would be liberated as part of the operation, and the new world - christened Avalon - would be explored and surveyed in detail, once the counter-attack was underway.
The only reliable way to access Avalon was via the air, and massive air ferrying efforts began, raw materials, equipment and personnel shuttled through the Tokyo Jupiter portal to establish an operating base on the other side. The Combined Expeditionary Forces had been formed, and they began to take the battle to the Invaders.
The Expeditionary Force arranged into units, squadrons and other such divisionary lines. Personnel and equipment from different nations were assigned together in new and radical ways of thinking appropriate to fighting a new enemy on a new world. Slowly the Expeditionary Force began to develop its’ own identity, here on the ‘other side’ away from the real world, back ‘there’, home, shore-side, of Earth, split by so many millions and millions of miles of space, yet only a few short hours of flight through the portal.
New production efforts were undertaken, old designs were re-tooled and re-equipped, pressed into service to fight new wars, as newer designs were held back for the defensive efforts on Earth's side of the portal, and refined, honed and developed for the next generation of combat against the Yerrill on their home turf, redeveloped with newly-emerging technology from reverse-engineered Yerrill technology and Avalonian knowledge.
The newly equipped Expeditionary Forces, with their ragtag assortment of rebuilt, reproduced, and re-engineered machines were sent through the portal, and became the first humans to set foot on an alien world.
Almost as soon as they arrived, the Expeditionary Forces were thrown into combat. Yerrill were waiting for them, and they engaged in battle, well in view of Avalonian work camps and settlements. The Expeditionary Force soon overcame the Yerrill threat, and in so doing, freed hundreds of Avalonians. They spread the word to their families and friends, and the Expeditionary Force learned about other camps and settlements.
Soon, the Avalonians came from miles around to see the developing base of the Expeditionary Force, many staying as they took advantage of the free handouts of food and aid, and of the safety in the wings of the Expeditionary Force.
A small town became established around the perimeter of the base, and soon became patrolled by security forces as the men and women of the Expeditionary Force went there to relax in their off-duty hours. Before too long, the Avalonian people also became part of the security details and forces, with others enlisting within the Expeditionary Force as the UN opened negotiations with the Avalonian people as true allies.
All of this became the backdrop for the ongoing war against the hostile aliens - now known as the Yerrill, from the local species - who it turned out had invaded this world in turn, bringing with them slaves from other places who had become part of the local population. The humans were the first ones to fight back any kind of effectively.
Among the Expeditionary Forces many squadrons are Hellcat Team of the 101st Tactical Fighter Wing. The relatively newly formed, 101st is one of the first squadrons to have both Avalonian and human pilots together, and to operate as a 'dispersed' tactical unit, it's fighters operating on numerous individual missions.
Though they don’t know it yet, they will find themselves at the heart of learning more about the Yerrill, about the locals of Avalon, and about the history of this war and how it started. And in doing so, will become a lot more famous than even they could imagine…