Both Kuat Drive Yards and Sienar Fleet Systems have long been regarded as leaders in the starship manufacturing industry. With cutting-edge technical developments and efficient, high-quality manufacturing procedures either could have easily claimed the title of producing the galaxy's best ships.
While both industrial powerhouses had extensive design and production facilities at various locations throughout the galaxy, they infrequently cooperated. Often, it was a matter of competition or outright "one-uppance" of one company over the other when it came to producing cutting-edge technology or receiving lucrative contracts. The rivals did share a particular star system in common, Selene, because of its location in the Core Worlds affording uninterrupted technological development, easy access to supplies and materials, and close proximity to the Imperial command structure (both companies' largest customer).
In 7 ABY, under the direction of newly-crowned Emperor Valak, the two companies were merged, in principle, at the Selene location and put under one Board of Directors. While their other governing entities still were independent of each other in the galaxy at large, the Selene facilities were unified to streamline production costs, reduce production time, and focus manufacturing efforts. Known as KDY-SFS within the Imperial sphere, this new union-on-paper would go on to produce most of the new starships and vehicles for the Empire's heightened efforts to wage war on the New Republic.
KDYSFS Ships for a list of ships produced by KDYSFS.