Welding is one of major jobs in shipbuilding and is directly related to the cost and quality of products. Therefore, the automation of the welding process in shipyards is vital to improve the productivity, and robots play an important role in it, giving an extra benefit of replacing the human labors in dangerous working environments. The sub-assembly line in shipbuilding is composed of 3 stages in general: (i) Fitting, (ii) Welding, and (iii) Finishing. In the fitting stage, operators place the base panels and stiffeners on the skid. Before performing the main welding process, the tack welding process is carried out in the fitting stage to place the stiffeners on the panel at the predefined positions, and approximate positioning of the panels is carried out using a fixed camera installed on the factory ceiling. The system for the sub-assembly line can be classified into 3 categories: (i) machinery system to perform the welding process, (ii) control system to govern the machinery system and to move the robots for welding, and (iii) management system to perform supporting roles such as running an off-line program to load CAD data of the welding panel, assigning the conditions of each welding line, and controlling the camera vision system.