A Heat-Seeking Missile seeks the heat generated by the engines of a spaceship. To be effective, it requires the pilot to be on an enemy's tail. Such missiles need to lock before fired. If the target shakes a heat seeker, the missile locks onto the nearest heat source.
The Claw Marks manual mentions Pilum FF and Spiculum IR by name, whereas in the entries of the above ships it gives only a generic "Heat-Seeking Missile(s)" without specifying the Javelin by name. The specification is given in the blueprints of the game package.
It tracks the target's heat signature and, as such, cannot lock onto anything but a target's engines and can be evaded simply by turning 90 degrees.