This paper proposes practical weapon target assignment (WTA) algorithms for a defense system to counter multiple targets concentrated within a narrow area, such as low-altitude rocket threats or drone swarms. Since the probability of kill (PK) is greatly affected by heading errors between launchers and targets in this type of engagement, WTA problems must first be formulated, considering heading error, to reflect more realistic engagement situations. Two WTA algorithms-a rotation-fixed strategy and a rotation strategy- are proposed based on this formulation. Moreover, we propose a method for determining launchers' initial orientation angles, based on a clustering approach, to further improve the engagement performance of the two algorithms. Numerical simulations were performed to demonstrate the effectiveness of the proposed methods.