Lancer-class fast-attack corvette
From Halopedia, the Halo wiki
The primary armament of the Lancer are rapid-fire naval coilguns, which allowed it to harass large Covenant ships from a relatively safe distance, and eliminate smaller vessels before they could get into plasma torpedo range. Its relatively small magazine capacity means that a typical strategy is for Lancer squadrons to "dump rods" early in the engagement and then attempt to disengage to behind the main fleet and replenish their stores.
The class’s limited endurance (both in terms of ship stores and fuel) restricted their use in wartime expeditionary operations, and most were relegated to internal patrol and planetary defense picket duties. Many were even stripped of their slipspace drives, with the extra space used for additional ammunition and crew comforts.