A locking system for locking a container to a vehicle includes a locking assembly mounted to a hoist frame and a striker assembly mounted to the vehicle chassis. The locking assembly has at least one hook for hooking over a frame member of the container. The hook has a center of mass that biases the hook to an unlocked position. The striker assembly strikes the hook at a location to move the hook against the bias of the hook's center of mass into a locked position in which the hook is hooked over the frame member of the container. As the hoist frame supporting the container is lowered, the striker assembly contacts the hook and rotates the hook against the bias of the hook's center of mass into the locked position. As the hoist frame is raised, the hook rises as well and loses contact with the striker assembly, thereby falling away from the hoist frame and unlocking the container. A positive or mechanical unlocking mechanism prevents the hooks from binding to the container.