a procession (of wagons or mules or camels) traveling together in single file; "we were part of a caravan of almost a thousand camels"; "they joined the wagon train for safety"
air passage provided by a retractable device containing intake and exhaust pipes; permits a submarine to stay submerged for extended periods of time
breathing device consisting of a bent tube fitting into a swimmer's mouth and extending above the surface; allows swimmer to breathe while face down in the water