“…Control design in the general case where nondiagonal matrix elements are also taken into account is not as difficult in a fully actuated case, but is nonetheless an active and difficult topic of research in the underactuated case [19,34]. Though many motion control algorithms have been developed for dealing with underactuated systems of the AUV and other marine vehicles in [13,14,[16][17][18][19][20]29,30,[34][35][36], little research has considered fore/aft asymmetry of the AUV model, the exceptions being [17][18][19][34][35][36]. In [17][18][19][34][35][36], details concerning the control performance differences of AUVs when comparing the nonlinear control method based on the symmetric model and that based on the non-symmetric model are not presented.…”