Interdictor cruisers, like their Vindicator-class cousins, had the appearance of small Star Destroyers. However, their lines were broken by four large globes housing gravity well projectors which mimicked a large mass in space, restricting hyperspace travel. Nearby vessels were automatically prevented from engaging hyperdrive, and any ship passing through the area via hyperspace were forced into realspace. From SW1ki, a Wikia wiki.