The problem of path following and formation control for underactuated 3-degrees-of-freedom surface vessels in the presence of unknown ocean currents is considered. The proposed controllers make the vessels asymptotically constitute a desired formation that follows a given straight-line path with a desired speed profile. This control goal is achieved in the presence of currents of unknown direction and magnitude. The proposed controller consists of an adaptive yaw controller, which makes every vessel converge to its desired path, and a surge controller, which guarantees formation assembly along the path with the desired forward speed. The results are illustrated by simulations.