Complex sentence: The United States first ICE X exercise in which a submarine surfaced and broke the ice was in 1958, and since then the United States has conducted more than 26 Arctic exercises, some in more recent years were Ice Exercise 2009.
Split into simpler sentences: The United States' first ICE X exercise in which a submarine surfaced and broke the ice was in 1958. Since then, the United States has conducted more than 26 Arctic exercises, including the Ice Exercise 2009.