Question: The Big Sandy Expedition was organized by a Union general who was also a United States what?
Context: Big Sandy is a town in Chouteau County, Montana, United States.  The population was 598 at the 2010 census.  Big Sandy, Montana, is where the Big Bud 747, the largest farm tractor in the world, was located from 1997 until 2009.  The Lewis and Clark Trail, following U.S. Route 87, goes through Big Sandy and in 2011 the town was named in a list of "Most Livable Small Towns" by Montana Outdoors magazine. Big Sandy Regional Airport (ICAO: KSJS, FAA LID: SJS) (formerly K22) is a public use airport located in southwest Martin County, Kentucky, United States.  The airport is nine nautical miles (17 km) northeast of the central business district of Prestonsburg, a city in Floyd County.  It is owned by the Big Sandy Regional Airport Board. The Big Sandy River is both an intermittent and perennial stream in Mohave and La Paz counties in northwestern Arizona in the United States.  It begins where Cottonwood Wash and Trout Creek converge in the Hualapai Indian Reservation east of U.S. Route 93 then flows past Wikieup south of Kingman.  The Big Sandy River then passes the Signal Ghost Town Site, meanders through the Arrastra Mountain Wilderness, and joins the Santa Maria River in Southern Mohave County to form the Bill Williams River.  The Bill Williams River then empties into Alamo Lake State Park.  The Big Sandy River is 55.7 mi long. William "Bull" Nelson (September 27, 1824 – September 29, 1862) was a United States naval officer who became a Union general in the Civil War. The Big Sandy River (also called Big Sandy Creek) is a 141 mi tributary of the Green River in Wyoming in the United States. The Big Sandy Expedition was an early campaign of the American Civil War in Kentucky that began in mid-September 1861 when Union Brig. Gen. William "Bull" Nelson received orders to organize a new brigade at Maysville, Kentucky and conduct an expedition into the Big Sandy Valley region of Eastern Kentucky and stop the build-up of Confederate forces under Col. John S. Williams.  This was done in three phases.  From September 21 to October 20, 1861, Nelson assembled a brigade of 5,500 Union volunteers from Ohio and Kentucky.  On October 23, the southern prong secured Hazel Green and the northern prong West Liberty.  The two prongs were consolidated at Salyersville (Licking Station) and they began the final phase on October 31.  This led to the Battle of Ivy Mountain on November 8 and the withdrawal of Confederate forces from Pikeville (Piketon) on November 9, 1861. Big Sandy Airport (FAA LID: 3U8) is a public use airport in Chouteau County, Montana, United States.  It is owned by the Town of Big Sandy and located one nautical mile (2 km) south of its central business district.  This airport is included in the National Plan of Integrated Airport Systems for 2011–2015, which categorized it as a "general aviation" facility. The United States Penitentiary, Big Sandy (USP Big Sandy) is a high-security United States federal prison for male inmates in Kentucky, near Inez.  It is operated by the Federal Bureau of Prisons, a division of the United States Department of Justice.  The facility also has a satellite prison camp which houses minimum-security male inmates. The Pikeville Cut-Through is a rock cut in Pikeville, Kentucky, United States created by the U.S. Army Corps of Engineers, through which passes a four-lane divided highway (Corridor B, numbered as US 23, US 119, US 460, and KY 80), a railroad line (CSX Big Sandy Subdivision), and the Levisa Fork of the Big Sandy River.  It is one of the largest civil engineering projects in the western hemisphere, moving nearly 18000000 cuyd of soil and rock, compared to the Big Dig (15 million cubic yards) and the Panama Canal (240 million cubic yards).  Dr. William Hambley, who served as mayor of Pikeville for 29 years, Robert H. Holcomb, Chamber of Commerce president, and Henry Stratton, local attorney, spearheaded the project. The Levisa Fork (also known as the Levisa Fork River or the Levisa Fork of the Big Sandy River) is a tributary of the Big Sandy River, approximately 164 mi long, in southwestern Virginia and eastern Kentucky in the United States.
Answer: naval officer