Systems for tethering an underwater vehicles using a low strength optical fiber tether. The tether system includes, a mechanical fuse that prevents a high load from acting on and severing the tether that is attached to the underwater vehicle, thus allowing use of far smaller cables than typically used. Upon separation of the fuse, a cable payout system pays out an optical fiber that keeps the underwater vehicle, typically a robotic craft, in communication with the surface vessel. The relatively light weight glass fiber may be reinforced and extended to lengths greater than 40 km allowing deep-sea exploration at depths up to 11,000 m.