Pacific, once known as Franklin, took its name from the Pacific Railroad, the only rail line from St. Louis to that point before the Civil War and, when its first division opened in July 1852, the westernmost point reached by any steam railroad in the United States. The railroad's main line, built in the 1850s, reached Jefferson City in 1855 and Sedalia by 1861, while its Southwest Branch began construction at Pacific in 1855 and was completed to Rolla in December 1860, making Pacific one of only two railroad junctions outside St. Louis in Missouri and a critical military resource when war began in May 1861. The first Union unit to occupy Pacific in force was the 9th Iowa Volunteer Infantry, which arrived on October 11, 1861, established Camp Herron, and remained on guard duty until January 1862 before joining the campaign that ended at Pea Ridge. Several companies of the 26th Missouri, composed largely of Franklin County recruits, also enrolled and trained at Pacific before going on to service at Vicksburg, Missionary Ridge, and Sherman's March to Savannah. Disease devastated troops stationed there in the fall and winter of 1861, killing more than 20 men of the 9th Iowa from measles, typhoid fever, chronic diarrhea, and related causes, while some Franklin County recruits of the 26th Missouri died in hospital during Christmas week of 1861 before they were even mustered in. War returned in 1864 during Price's Expedition, when a Confederate force of 12,000 cavalry and mounted infantry under former Missouri governor Maj. Gen. Sterling Price entered southeast Missouri on September 16, moved north in three columns, and after the Battle of Pilot Knob reached the Southwest Branch at Leasburg on September 29 and at St. Clair on September 30. A military hospital was established near Pacific in 1861 under the Western Sanitary Commission of St. Louis as one of several facilities for sick and wounded soldiers unfit to travel to St. Louis hospitals, and Catholic Sisters of the Holy Cross from South Bend, Indiana, served there as nurses; the order also staffed the first hospital ship in American history at Mound City, Illinois, and came to be regarded as forerunners of the U.S. Navy Nurse Corps. Pacific was also tied to an innovation in military medicine when, by most accounts, the world's first railroad hospital cars were outfitted in September 1861 by order of Maj. Gen. John Fremont and placed in service on the Pacific Railroad between Jefferson City and St. Louis. Fremont, celebrated as the Pathfinder of the West, had earlier explored western routes in 1848 and 1853 in support of Senator Thomas Hart Benton's search for a railroad route that would place Missouri at the center of commerce with California, then became a Union major general in July 1861 and briefly commanded the Western Department in Missouri. During his short and scandal-ridden tenure, as his army prepared in October to move south from a base on the Pacific Railroad near Tipton, the 9th Iowa was advanced to Pacific to protect his supply line. The war's effects on Missouri railroads ultimately ruined Benton's dream of a railroad to the Pacific and helped clear the way for the northern route that became the Union Pacific. In 1866 Fremont led investors in acquiring the Southwest Branch to continue building westward, but after only a few miles were added beyond Rolla he defaulted, losing the venture and, it is thought, the fortune he had made in early California; the line later passed to another company and became the foundation of the St. Louis-San Francisco Railway.