This paper investigates distributed \(H_\infty \) time-varying formation tracking of three-degree-of-freedom (3-DOF) unmanned surface vehicles within a singular control framework under jointly connected switching topologies. To tackle the associated control challenges, a distributed integral sliding-mode protocol is constructed together with a nonlinear disturbance observer(NDO), which is designed to handle time-varying external perturbations whose residual is \(L_2\) -integrable. Then, an energy-based \(H_\infty \) criterion is imposed to restrict the closed-loop gain from residual disturbances to formation-tracking errors. Furthermore, by employing Laplacian decomposition under joint connectivity and a Cauchy-type convergence argument, sufficient linear matrix inequality (LMI) conditions are established to ensure admissibility as well as the feasibility of the prescribed time-varying formation tracking task. The resulting distributed gains are explicitly computable and only require local relative-state information. Finally, numerical simulations are provided to demonstrate the effectiveness of the proposed singular control approach.