Divad was an EF76 Nebulon-B escort frigate used by the Galactic Empire during the Galactic Civil War.
Divad and the CR90 corvettes BB 45 and SB 35 formed the escort force of the first Death Star and were specifically tasked with protecting the communications satellite coordinating its defenses in the Yavin system.
In preparation for their assault on the battle station, Keyan Farlander, his two X-wing wingmen and an escort of two R-22 Spearheads were dispatched to destroy the comsat. While Farlander's wingmen held off Imperial fighters, Farlander ignored the threat and headed straight for the satellite, destroying it with a proton torpedo before quickly returning to base. However, both his wingmen were shot down and the pilots had to be rescued later.
The destruction of the comsat denied access to Imperial reinforcements and left it open to direct attack by unsupported starfighters. It also succeeded in slowing down the Empire's preparations for the battle, allowing the Alliance longer to analyze the Death Star plans brought to them by Leia Organa and to plan their strategy.
Behind the scenes
The Death Star's support fleet is not shown in Star Wars: Episode IV A New Hope and no other canon sources say that such forces ever encountered Rebel fighters before the attack on the Death Star. It is possible that the escort had already left when we see the scene of the fleet moving to the Death Star or that the over-confident Empire held the support ships back so as not to distract from the Death Star's expected victory. Either way, the main bulk of the Rebel fleet would be free to move without further encounters.
Note that in Star Wars: Rebel Assault, we see that the Death Star was orbited by an unnamed Star Destroyer that launched waves of TIEs to the Blue Squadron ships. It is possible that this was also part of the support fleet although, because of Rebel Assault's ambiguous canonicity, this event may not be canonical.
Divad is perhaps an anagram for David.