Hiroshima was a city in Japan that was devastated by a nuclear bomb dropped by the United States on August 6, 1945, towards the end of World War II.
On the eve of the September 11, 2001 attacks on New York City and Washington, DC, Gary Seven reflected that he would not stop the events from occurring, just as he would not stop the the bombing on Hiroshima or the bombing of Pearl Harbor on December 7, 1941. (TOS short story: "Assignment: One")
While at Starfleet Academy in the late 2230s and the early 2240s, Christopher Pike studied Hiroshima. (TOS novel: Burning Dreams)
Admiral Heihachiro Nogura had an ancestor who was killed by the blast at Hiroshima. (TOS novel: The Pandora Principle)
The USS Hiroshima was named for the city. (ST reference: Star Trek Encyclopedia)