Line of sight (LOS) navigation is a simple but extremely important algorithm in controlling autonomous underwater vehicles (AUVs), unlike trajectory tracking algorithms, LOS focuses on the trajectory of the controlled object regardless of travel time. It is a path-following algorithm designed to ensure that the AUV follows the desired trajectory by continuously adjusting its heading angle based on waypoints and reference points (LOS points). By tuning control parameters, we determined the LOS point to converge on the trajectory over time, we found that the algorithm improves stability, performs well under standard environmental conditions with minimal external disturbances. To apply the LOS algorithm to an AUV, we developed a MATLAB program to interface with a 5-DOF dynamic model, the program outputs which includes thrust force, motor speed and rudder angle was then used to execute Hardware-in-the-Loop (HIL) with three different trajectory shapes including rectangular, circular, and zigzag to test the convergence and response of the actuators. The results we obtained show that the vehicle successfully tracked these paths with high accuracy, ensuring that the rudder angles converged over time. Our study highlights the practicality of LOS-based navigation for real-world applications, including environmental monitoring and maritime surveillance.