The Javelin was an aquatic craft armed with surface-to-air missiles for targeting airspeeders and starships. They were used by the Rebel Alliance to accompany water fleets or water transport vessels to guard against strafing and to provide anti-air defense to Rebel shipyards.
The Heavy Javelin was an upgraded model of the standard Javelin. Instead of one surface-to-air missile launcher, the Heavy Javelin had two.