Spoiler warning for anyone who hasn’t played the tutorial yet, but I wanted to talk about what we can learn from it.
So during the cutscene, we see Agryna mention to you that Laconia changed everything, and it’s sounds like she’s referring to it as an event that’s named for its location.
Which makes sense as Laconia is a planet in the same system as Arcadia. It shows up in the Rion Forge books, but not in any way that would prompt Agryna’s statement.
It’s possible something more recent happened there with the Created or Banished.
Then again, the name could apply to any new location or ship, etc, but either way, there is now an event that gets referred to as Laconia.
Then Agryna is informed that Infinity is missing, along with the ring, and later Chief and other Spartans. This would suggest that the two events are not the same, but that Laconia is a recent event that shifted the balance of the war, and not in the favour of the UNSC.
But we can also assume that the tutorial is taking place shortly after the event which leaves Chief in space, so roughly six months prior to the campaign.
So we have 2 events; Laconia and the ‘6 month prior’ event.
We also know the Rubicon Protocol will cover the Banished invasion of Zeta Halo against the UNSC. This is likely what Escharum is referring too in his trailer speech to Chief.
Based on this, I’d like to present my current Tinfoil Theory.
In terms of a timeline, the UNSC controls Zetal Halo at the time of Halo 5. Some time after, the UNSC/ONI decide to establish another Spartan training facility on solid ground. Later, the Banished invade the halo and scatter the UNSC. When all is but lost, Cortana arrives and takes control of the halo, moving it to Laconia where she is able to use it to win a devastating victory against the UNSC, possibly whipping out a colony and a vast number of ships in the system.
This became known as Laconia.
Following this, ONI decide that it’s time to deploy the Weapon, and send Infinity, Chief and the Spartans to Zeta Halo to defeat Cortana.
Something goes wrong, and the halo ends up jumping to an unknown location. The ring gets destroyed, a guardian goes down, Infinity may have been destroyed, and Chief winds up in space along with the Pilot.
Shortly after,
We arrive at the Spartan training facility, as Agryna learns that the ring has disappeared, and promptly leaves, presumably meet with commanding officers to figure out what to do now.
Then, 6 months later, the campaign picks up, with the Pilot finding Chief, and them attempting to tack back the ring.