The second Watchtower was an orbital command center for the Justice League. It was built to replace the original Watchtower that was sacrificed to save the Earth during the Thanagarian invasion. Several other, smaller annexes were in orbit close by.
This Watchtower was much larger to accommodate the expanded League following the Thanagarian invasion. In addition to the League members, the Watchtower also employed an extensive support staff. The base was equipped with wide hangar facilities, including at least nine separate landing pads to support the fleet of improved Javelins. as well as large cargo and transports for humanitarian emergencies.
It also housed the powerful orbit-to-ground Binary Fusion Generator which was the power supply for the entire facility; However the generator also doubled as a weapon. Housed in its lower decks, in the event of an attack similar to the Thanagarian invasion. Firing the weapon required tremendous amounts of energy, and was done sparingly if at all. After firing, the Watchtower's power systems required one hour to recharge and restore primary power to the station. Until then, the station would be on strictly emergency power, life support and artificial gravity. Communications were largely blacked out beyond a special communications link to the President of the United States.
The Watchtower's center was a promenade with a monitor perch. Around it were an operations pit and a teleport platform. It was directly adjacent to the hangars and to several hallways that lead to storage facilities, the commissary, an infirmary, laboratories for research and repair, and living quarters that catered to each member's living conditions.
The Watchtower was originally slated to be decommissioned after the Cadmus incidents, but instead was used in tandem with the League's new ground-based headquarters, the Metro Tower. However, the station's main energy cannon was taken permanently off line to avoid a repeat of the dangerous incident where Lex Luthor hijacked the weapon long enough to make an unwanted firing on Covenant, New Mexico and frame the League for it.
After the League was expanded, J'onn took the role of the League's official coordinator, keeping watch on a global scale and handing out assignments based on the availability of hero personnel and the best match of abilities to situations. He was presumably picked for this job because of his intelligence and wisdom, but also because, as an alien, he was the one most able to spend an indefinite amount of time in the Watchtower. It also assured that the main control room and teleport pads were under constant guard by someone who could handle small and big threats on his own.
Binary Fusion Generator
During the Thanagarian invasion, the first Watchtower was destroyed when Batman was forced to take it out of orbit and crash it into the Thanagarians' Hyperspace bypass generator, to prevent the total destruction of Earth.
In order to prevent a similarly powerful threat from appearing on Earth in the future, the second Watchtower was designed to direct the entire output of its nuclear power plant into a single energy blast, according to J'onn, it's "a gun with the punch of a small nuclear weapon".
The Generator was first used during the Dark Heart crisis, to delay the advance of the Heart's probes by digging a trench in the desert—blasting the heart directly would scatter the pieces and widen the threat.
Though the installation of the cannon made strategic sense after the Thanagarian invasion, it proved to be one of the expanded Justice League's most inflammatory actions. Its existence (and the fact that the League had kept it a secret until then) only reinforced the opinion of many, such as General Wade Eiling, that the League was a potential threat to the world. Eiling and Amanda Waller, both members of Project Cadmus, pointed to the Generator's existence in defense of their attempts to counteract the League.
Knowing this, Lex Luthor cannily used the Generator as a "flashpoint" to discredit the League, taking remote control of it and using it to fire down on Cadmus headquarters, causing massive devastation in the surrounding area. Though there were no fatalities, tempers ran high.
The Generator could fire a beam of energy at Earth with pinpoint accuracy, though not enough to shoot down a missile in flight. The major disadvantage of using it was that it drained all of the Watchtower's available energy for an hour, disabling its sensor devices and all available functions, except minimal life support and communications (meaning it would take the League an hour to even be able to assess the effectiveness of the blast).
The Watchtower also provided quarters to house various members of the League either temporarily or permanently. Huntress maintained quarters aboard the station prior to her dismissal, as did Question 
J'onn J'onzz undoubtedly maintained permanent residence aboard the Watchtower given he spent 2 years without ever visiting Earth. Wonder Woman also maintained quarters aboard the Watchtower, judging by the level of decoration it was on a permanent basis.
Standard quarters consisted of a bed large enough to accommodate a two adults with attached end table. Column lighting, a computer terminal and desk and clothing/equipment locker.
Given the Watchtowers size and complexity, a sizeable staff and hero complement; some of whom reside aboard the station permanently of course need to be fed. As such the Watchtower maintained a cafeteria where public meals by heroes could be taken. However Superman used the word Commissary, implying that while the Cafeteria was open, the food must have been purchased.
High Security Storage Area
Many items of conquered enemies were stored in the Watchtower:
- The Annihilator;
- A Gorilla City hover bike;
- Grodd's mind control helmet;
- Pieces of Lex Luthor's giant robot;
- Pieces of Toyman's Giant Robot
- Lex Luthor's battlesuit;
- Several Thanagarian melee weapons;
- Lex Luthor's energy disrupter.
- ↑ 1.0 1.1 1.2 Justice League Unlimited, "Initiation"
- ↑ 2.0 2.1 Justice League Unlimited, "Dark Heart"
- ↑ 3.0 3.1 3.2 3.3 3.4 Justice League Unlimited, "Flashpoint"
- ↑ Justice League Unlimited, "Fearful Symmetry"
- ↑ 5.0 5.1 Justice League Unlimited, "Divided We Fall"
- ↑ Justice League Unlimited, "To Another Shore"
- ↑ Justice League, "Starcrossed, Part III"
- ↑ 8.0 8.1 Justice League Unlimited, "Question Authority"
- ↑ Justice League Unlimited, "Patriot Act"
- ↑ 10.0 10.1 Justice League Unlimited, "The Doomsday Sanction"
- ↑ Justice League Unlimited, "Panic in the Sky"
- ↑ Justice League Unlimited, "Ultimatum"
- ↑ Cite error: Invalid
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- ↑ Justice League Unlimited, "Hawk and Dove"
- ↑ Justice League, "The Brave and the Bold, Part I"
- ↑ Justice League, "The Brave and the Bold, Part II"
- ↑ 17.0 17.1 Justice League, "Legends, Part I"
- ↑ Justice League, "Injustice For All, Part II"
- ↑ Justice League, "Tabula Rasa"
- ↑ Justice League, "Only A Dream, Part I"
- ↑ Justice League, "A Better World, Part I"
- ↑ Justice League, "Starcrossed"
- ↑ Justice League, "A Better World"