The Javelin heat-seeker (HS) is an inexpensive, simple weapon that has served in various armed forces since the late 1900s. The engines of fighters and capital ships generate significant heat, a fact that the HS uses to its advantage. The operation is simple - the missile tracks down the thermal signature of the target's engines. This requires the lock to be acquired from the rear. Heat-seekers, along with dumbfire missiles, are the most common missile carried on fighters.