PQ-1 was a Federation convoy.
In late 2374, the USS Defiant escorted PQ-1 to the Vegan system. As she knew many of the freighter captains, Kasidy Yates took the job of convoy liaison officer. (DS9: "The Sound of Her Voice")
According to Ronald D. Moore, PQ-1 was a homage to World War II Convoy PQ 1. (AOL chat, 1998)