Same as Polychorus. Kurt had two of them apparently, and used them on the Unplugged show. However, I don't know what songs he used it on. I don't think he used it one any songs, but Guitar World says that he was arguing with MTV techs over the various qualities of the Echoflangers.
THE FORGOTTEN MARINES OF TARAWA. During late-November 1943 one of the most savage battles in the history of the Marine Corps took place on the tiny island of Betio, located in Tarawa Atoll. The capture of this island took three days and cost the lives of 990 Marines and Navy Corpsmen. In addition to these, another 2,200 were wounded.
Tarawa is an atoll and the capital of the Republic of Kiribati, in the central Pacific Ocean. It comprises North Tarawa, which has much in common with other, more remote islands of the Gilberts group; and South Tarawa, which is home to 50,182 as of 2010 - half of the country's total population. The atoll is best known by outsiders as the site of the Battle of Tarawa during World War II.