A cable containing an optical fiber is used to transmit data between an underwater remotely operated vehicle (ROV) and a support vessel floating on the surface of the water. The ROV pulls the cable through the water and as the ROV dives away from the support vessel, the optical fiber is released from the support vessel. Excess tension in the cable can damage the optical fiber and the tension can be highest close to the ROV. To prevent potential damage to the optical fiber, the ROV can store a portion of the cable and release the cable if the detected tension approaches the maximum working load. When the tension drops to a lower safe level, the release mechanism can stop releasing the cable.