The Lancer-class frigate was a capital ship used for anti-starfighter operations in the Imperial Navy.
Imperial starships had long focused on ship-to-ship combat capabilities, relegating smaller capital ships to planetary defense rather than picket duty. As Rebel Alliance pilots learned to exploit the major weaknesses of Star Destroyers, commonly called "Trench Run Syndrome", Imperial officers grew increasingly concerned over the growing relative effectiveness of these heavily armed and shielded starfighters. After the first Death Star’s destruction at the Battle of Yavin by handful of Alliance starfighters, the need for greater starfighter defense was clear.
Admiral Drez envisioned the Lancer-class ships, and proposed using them to screen enemy starfighters to allow dominant Star Destroyers to pummel enemies in ship-to-ship combat. With approval from the Imperial Starfleet, Kuat Drive Yards designed and developed the ship. The final iteration ran a slim 250 meters with twenty quad-laser cannon batteries designed specifically for starfighter hunting, but required a relatively large crew of 850.
The Imperial Starfleet, however, found the Lancer-class too expensive for full fleet deployment. A few frigates made it into various fleets, but most admirals preferred to use, and subsequently lose, their TIE starfighters as anti-starfighter options. As a result, most Lancer-class frigates, like smaller ships before them, were assigned to planetary defense and rear guard operations.