The McAllister C-5 Nebula was a protostellar nebula in the Alpha Quadrant of the galaxy. This nebula was the location of a conflict between the Cardassian Union and United Federation of Planets in the 24th century. In 2369, the nebula was used to hide a Cardassian fleet which was faced down by the crew of the USS Enterprise (NCC-1701-D) under the command of Edward Jellico. Commander William Riker, flying a shuttlecraft, managed to plant mines on the outside hulls of the Cardassians' vessels, a move that was used to force the withdrawal of Cardassian forces from the nebula. (TNG episode: "Chain of Command")

In 2390, another Enterprise, the 1701-E, conducted research at the McAllister C-5 Nebula. Scans revealed quantum singularities which hinted at the presence of Species 8472 in the area. (ST website: The Path to 2409)