Cabin John, village (1990 pop. 5,341), Montgomery co., central Md., on the Potomac c.10 mi/16 km above Wash., D.C.; 38°58'N 77°09'W. Site of Cabin John Bridge on McArthur Blvd., a single masonry arch built in 1857–1863 to carry water from the Great Falls of the Potomac to Wash. The conduit, 100 ft/30 m high and 220 ft/67 m long, still carries 20% of the D.C. water supply as vehicular traffic moves over the bridge. Nearby is the Naval Research and Development Center, started in 1936, which contains a towing tank, the aquatic equivalent of a wind tunnel to test scale models. A biological observation station is on Plummer Island.
