- Big Diomede Island or Tomorrow Island (Russian: Остров Ратманова, romanized: ostrov Ratmanova; Ratmanov Island, Chukot: Имэлин; Inupiaq: Imaqłiq) is the western island of the two Diomede Islands in the middle of the Bering Strait. The island is home to a Russian military base which is located midway along the island’s North shore. The island is a part of the Chukotsky District of the Chukotka Autonomous Okrug of Russia. The border separating Russia and the United States runs north–south through the 2.5 mile wide strait that runs between the two Islands.