site of a U.S. Navy submarine base through the late 1990s. It operated as a nuclear weapons handling facility servicing fleet ballistic submarines until the advent of the larger Trident submarine-launched ballistic missile. Since the s required a deeper draft, the nuclear weapons handling had to move to another facility. Crossings Formerly traffic across the river was limited to ferries. The John P. Grace Memorial Bridge was opened for service on August 8, 1929, as the automobile and trucks became an increasingly important mode of transportation. It was named for the commissioner who inspired the state's highway system. The State of South Carolina built a parallel span that opened April 29, 1966, the Silas N. Pearman Bridge constructed a few yards (meters) to the south. For more than a quarter of a century, the only connection between Charleston and its rapidly growing northern suburb of Mt. Pleasant was by these two bridges. In 1992, the Don Holt Bridge was completed a few miles upriver as part of the I-526 corridor, and became the third bridge to span the river. The cable-stayed Arthur Ravenel, Jr. Bridge (or "New Cooper River Bridge") opened to traffic on July 16, 2005, to replace the two older bridges. Demolition of the Grace and Pearman bridges began shortly afterwards and was completed in late 2007. A popular 10k run across the bridge is held each spring, and is known as the Cooper River Bridge Run. Though both bridges are modern in every respect, the Holt and Ravenel bridges carry all motor vehicular traffic across the river in the metropolitan area. Further north, the Dennis C. Bishop Bridge carries US 52-US 17 Alternate traffic across the Tail Race canal just below the Pinopolis Dam on Lake Moultrie in northern Berkeley County. A CSX Transportation trestle bridge traverses the upper reaches of the West Branch, below the Pinopolis Dam. Another rail bridge crosses the Tail Race Canal less than a mile below the dam. References External links Cooper River Bridge Cooper River Bridge Run and Walk Rivers of South Carolina Rivers of Charleston County, South Carolina Rivers of Berkeley County, South Carolina