Captain Loomis was a 24th century Starfleet officer who served in the Dominion War.

After the Federation Alliance captured the Chin'toka system in 2374, Loomis and his crew were assigned to protect a Dominion communication array on AR-558. He was later killed by the Jem'Hadar, as was his second in command, Commander Parker. (DS9: "The Siege of AR-558")

This character was only mentioned in dialogue.
According to the Star Trek: Deep Space Nine Companion, the new characters written for "The Siege of AR-558" were named after cast and characters from the 1962 war film Hell Is for Heroes. In Loomis' case, his name was an homage to Joseph Hoover's character in the movie, who was also a captain (albeit an army captain, i.e. the equivalent of a Starfleet lieutenant).
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