RALEIGH - On a grassy field along Garner Road, a sleek UH-1 Huey helicopter swathed in the black and silver of the N.C. State Highway Patrol sits with its nose pointed due south.

Decades ago and thousands of miles away, Sgt. Chuck Boyd flew the UH-1 over the jungles of Vietnam for the Army. These days he flies over the woods and forests of North Carolina for the Highway Patrol, searching for a very different enemy: marijuana.

During these summer months, the height of "drug season," Boyd and three other pilots will each spend roughly three days a week scouring the state …