Doctor Strange (vol 2) #70 NM

Deadly Exchange; Doctor Strange's preparations for his infiltration of the Dark Dimension are interrupted when representatives of the U.S. Army come to him with a problem of various pieces of artillery being mysteriously swapped with primitive and monstrous equivalents in the blink of an eye; When Strange heads to the latest occurrence, he recognizes the spire that replaced a nuclear missile silo as belonging to the world of Kobar, whose warlord he had previously made swear off attacking the Earth; Strange travels to Kobar and finds that the warlord Chaynn is using the wizard Tymon's magic to borrow Earth weaponry so that they can study and replicate it for their own purposes.