Soon after reconstruction began on the crashed ASS-1, the United Earth Government ordered construction to begin on a fully human-designed version, designated the SDF-2. Construction began on the Moon. At the time of the Zentraedi attack, the SDF-2 was 50% completed. Construction halted for a few months after the Rain of Death, but was resumed aboard the newly-captured Robotech Factory. The ship was nearly completed, only lacking Fold Drives. It was decided to transfer the drives from the SDF-1, and so the SDF-2 was landed back-to-back with the SDF-1, in Macross Lake. However, days later, Khyron attacked in a suicide run, destroying both Battle Fortresses. The two vessels, and Khyron's ship as well, were buried to prevent nuclear contamination of the surrounding area.
The SDF-2 is difficult to distinguish from the SDF-1, but there are differences. The most obvious one is that the SDF-2 is 40% larger, almost a full mile long. It also has ARMD platforms connected, instead of the SDF-1's aircraft carriers.
Like the SDF-1, the Battle Fortress also has Destroid, Veritech, and other complete manufacturing facilities on board. Thus, Mecha can be repaired and constructed on the SDF-2.