From Halopedia, the Halo wiki
A hardpoint is a point on the outer hull of a warship designed for affixing external attachments to the ship. The term is also applied to a standardized connector system on UNSC warships, allowing them to easily dock and link systems with another ship.
Newer UNSC warships have hardpoints enabling a ship of similar size and density to dock and link systems. Located on the dorsal and ventral sides of the ship's hull, these points can be used to combine engine power, telemetry, stabilize, and link computer or AI systems in case the ship is too crippled to move under its own power. Another UNSC vessel can then use its own hard points to dock with the wounded ship, link systems and carry it away (presumably to a repair platform or safe zone).
During the Raid on Reach in September 2552, Cortana used the captured Covenant flagship Ascendant Justice to dock with the disabled and abandoned UNSC Gettysburg. Since Covenant and UNSC systems are incompatible, Cortana used the Gettysburg's service drones and the Ascendant Justice's Engineers to adapt their power uplinks.
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