The SDF-1 is the reconstructed spacecraft of Zor, the creator of Robotechnology. In the shattered hulk of the alien vessel, the humans were able to gather enough information to achieve great technological advancements. The Destroids And Veritech Fighters were the first triumphs of this new "Robotechnology". The crowning achievement was the complete reconstruction of the spaceship itself, the SDF-1.
The SDF-1 retained the rudimentaries of its original design, but many changes and modifications were made. Some were made out of necessity, like the additions of the two battleships. Daedalus and Prometheus, as the arm-like appendages. Likewise, the inclusion of the civilian populace of Macross Island was an unplanned modification. Other modifications were added as new discoveries were made. The pinpoint Barrier System was one that was later developed into a full force-field that could encircle the entire battle fortress. Its most unique feature was the Modular Transformation, which would allow it to conform to the most appropriate form needed for the combat situation.
The Battle Fortress also has Destroid, Veritech, and other complete manufacturing facilities on board. Thus, Mecha can be repaired and constructed on the SDF-1.