Offshore floating platforms used for oil and gas production are moored to the seabed by enormous metal chains. Current practice involves bringing the chain on deck for visual inspection, taking it ashore for non-destructive testing (NDT) or inspecting it on site using remotely operated vehicles. However, these techniques have proven unreliable and subject to human error. The EU-funded project 'Autonomous robotic system for the inspection of mooring chains that tether offshore oil gas structures to the ocean floor' (Chaintest) provided the solution by building a robot that can crawl along chains resting both above and below water for routine safety inspections. The device can test for cracks, corrosion and bent and elongated chain links. The robot removed rust and marine growth to conduct NDT using alternating current field measurement (ACFM) and ultrasonic guided wave (UGW) testing or low-frequency resonance techniques. Field trials were conducted at an indoor seawater facility at Brest in France. An autonomous robot system will make a significant contribution towards environmental protection and worker safety by improving the inspection of mooring chains used for tethering offshore floating production platforms.