The acronym SDF stands for Super-Dimensional Fortress during the earlier Robotech Wars, and Shadow-Dimensional Fortress in the later wars (referencing the addition of Shadow technology). This designations represents particular technological advancement for human starship technology, and is only held by the most powerful starships of human construction (or re-construction). There are four SDFs used during the Robotech Wars:
The Macross was originally Zor's battle-fortress, which crash-landed on Earth in 1999. The ship was rebuilt using hybrid alien and human technology, and served humankind during the First Robotech War. The SDF-1 was destroyed alongside the SDF-2 during Khyron's assault against New Macross City. Its remains are buried under one of three mounds at the abandoned site of New Macross City during the Second Robotech War (SX Point 83).
The SDF-2 was originally supposed to lead the mission in search of the Robotech Masters. It was almost entirely of human construction, built after the end of the First Robotech War. The SDF-2 was destroyed alongside the SDF-1 Macross during Khyron's assault against New Macross City. Its remains are buried under one of three mounds at the abandoned site of New Macross City (SX Point 83).
The Pioneer was constructed from hybrid human and Zentraedi technology after the loss of the SDF-2. It became the flagship of the Pioneer Expedition and the Robotech Expeditionary Force. The SDF-3 left Earth in 2022. It was supposed to rendezvous with the SDF-4 over Earth during the Third Robotech War in 2044, but became trapped in the Omicron Sector.
The Liberator was constructed in deep space during the Pioneer Mission. It was first used during the first battle on Praxis, and is specifically designed to combat Invid. In the absence of the SDF-3, the SDF-4 was the flagship of the United Earth Expeditionary Forces during the Battle of Reflex Point, the final battle of the Third Robotech War.
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