Plied yarns may themselves be plied together, producing "cabled yarns" or "multi-stranded yarns". Steamboats plied the Red River, and stevedores loaded and unloaded cargo. It stitched together and rigged the dhows that plied the Indian Ocean. The threads may be plied to form yarn. Such vessels plied both the Nile and the Mediterranean coast. Throughout the centuries Karelian traders have plied the Pielisjoki River. Army communicators sometimes plied their trade aboard Navy and civilian ships. His captors then plied him with drugs and alcohol. Prostitutes have long plied their trades to the military in many cultures. He was plied with both alcohol and Valium before he was strangled to death. The route was originally plied by fifteen horsecars, each pulled by four horses. Gacy plied Voorhees with alcohol and persuaded Voorhees to perform oral sex upon him. Hackney coaches plied there as in the streets. Double-decker buses plied route services in Sydney from the 1920s until 1986. A total of four submarines have plied the depths of Lake Geneva.