Anchor Handling Tug Supply (AHTS) vessels are mainly built to handle anchors for oil rigs, tow them to location, and use them to secure the rigs in place. AHTS vessels sometimes also serve as Emergency Response and Rescue Vessels (ERRVs) and as supply transports. Many of these vessels are designed to meet the harsh conditions of the North Sea, and can undertake supply duties there between land bases and drilling sites. They also provide towing assistance during tanker loading, deepwater anchor handling, and towing of threatening objects.