Mirror universe
(coexisting on another dimensional plane)
(coexisting on another dimensional plane)
Sopwith Camel
The Sopwith Camel was a type of airplane used in the mirror universe on Earth in World War I. (ENT: "In a Mirror, Darkly" opening credits)
Although not mentioned by name, the Sopwith Camel appeared in the opening credits, indicating the craft was manufactured and used in that universe.