The SD Platform was the primary target of the Helghan Empire's invasion. With laser defense systems capable of cutting right through the hull of a UCA Cruiser, it could very much negate the UCN's military superiority. With this knowledge in mind, the Helghast planned to destroy the reinforcement cruisers sent to the ISA from the UCN utilizing the SD Platform; however, Jan Templar and his squad were able to disable the Platform before it had a chance to annihilate the reinforcements (although the Platform did manage to destroy two Cruisers before it was deactivated).
The SD Platform was only part of an Orbital Defense Network that surrounded the space around the planet Vekta; this Network was made up of even more SD Platforms that linked up to one another via computer networks. Once built, the ISA had no more need for their Navy to stand guard (or so they thought), and slowly demilitarized. Seeing this as the perfect opportunity to strike, the Helghast made plans to invade Vekta.
When the Helghast Third Army began their invasion of Vekta, the ISA was relying on their SD Platforms (which would have easily torn the many Helghast cruisers apart) to defend them. However, due to the actions of the spy General Stuart Adams, the Orbital Defense Network was shut down, and the Helghast were able to make successful landings on Vekta's surface.
After taking control of much of the planet, General Adams reactivated the SD Platforms so that the Helghast could use them to obliterate any Vektan cities that still resisted their power.
Knowing that the ISA would send a distress call to the UCN, the Helghast made plans to once again utilize the SD Platforms so that they could easily destroy any reinforcements the UCN sent. This plan would have succeeded, if not for the actions of Jan Templar, Sergeant Rico Velasquez, Colonel Gregor Hakha, and Luger. This small squad successfully shut down key systems of the Orbital Defense Network, giving the UCN fleet the time they needed to destroy the SD Platforms. The UCN fleet lost two cruisers in this assault, but would have surely lost more if not for the actions of Templar's squad.