"When did the UN Navy become a cargo service?" "I believe it was just after a certain organization was established."
The unofficial (official?) name of the cross-shaped container that contains Unit-01 found at the beginning of Evangelion 3.0, floating in low orbit above a damaged Earth. The Tesseract unfolds to reveal several long tentacle-like arms made of metallic squares, which light up and begin to attack Unit-02'. Upon Unit-01's Awakening, the arms are destroyed, but the Unit remains inside the Tesseract for the duration of its appearance on screen. It is unknown when and how Unit-01 was retrieved upon returning from orbit.
The Tesseract contains the new Nerv logo on one side. It is evidenced from the various difficulties during Operation US that the intention was to make retrieval of Unit-01 difficult, and that placing the Unit in orbit was a known way to keep Wille from obtaining it.
The various implications of the Tesseract and its placement show that Nerv found Shinji's distance from Earth necessary. It's possible that there was a recurring fear of another Impact, and so keeping Shinji from Earth would prevent the disastrous effects thereof once again. However, Wille's need to retrieve Shinji and the risk of bringing Eva-01 back to Earth directly contradicts their very purpose--to prevent more Impacts. However, Misato mentions in 3.0 that Wille will "ensure your safety" to Shinji. It's then possible that Wille retrieved Unit-01 to get Shinji out of it, thus inhibiting an Impact, where Nerv may have gotten to the Tesseract first to initiate it.
Because Nerv seems to be responsible for creating the Tesseract, it can be assumed further that, by including traps inside it, they foresaw the presence of enemies in the future after its creation. Therefore, we can assume that the Tesseract may have been built after Wille came into existence, so as to shield Unit-01 from Wille's plan to "destroy Nerv's Evas".
The Tesseract appears as eight cubes combined to form a cross-like structure, with what appears to be a fence-like structure around the perimeter of the top and bottom of the device. In contrast to other crosses that appear in Evangelion canon, which are bright, thin and sport a rainbow, this cross in particular is black, solid and is a symbol of restraint, not victory.
One of the arms opens up and unfolds into four square-based tentacles that are mirror-like on the other side, and the other arms open up as well. Inside one of the arms is an Evangelion Mark.04 drone, which Unit-01 then destroys. It can be assumed that these were traps set for anyone wishing to release Unit-01 and not an integral part of the system.
Upon cracking open, Unit-01's eye can be seen glaring at Unit-02', surrounded by red matter, not unlike the environment of Third Impact. The inside appears very distorted and the nature of its contents cannot be known. Exactly what mechanisms are in place to restrain Unit-01 and how they prevent activity are also unknown.