In March, after general Henry Wager Halleck had been given top command in the West and Grant had been made a major general, Grant's Army of the Tennessee consisting of 42,000 troops, under orders from Halleck, was on the way to Corinith, Missippi, a strategically important railroad center. Union general Don Carlos Buell was marching down from Nashville with his Army of the Ohio made up of 25,000 troops. Grant positioned his troops on the western bank of the Tennessee at Pittsburg Landing with most men in camp near Shiloh Church, where he waited for Buell for almos a month. Grants men called the camp, which had been cold and wet at first, "the Tennessee Two-Step." The Confederate army, which was stationed at Corinith, two miles inland, were suffering from the same weather and called it "the evactuation of Corinith." Grant was caught off guard by the Confederate Army of the Mississippi, led by Pierre Gustave Toutant Beauregard and Albert Sidney Johnston(killed 6 April), the one who decided to attack before Buell arrived. Buell, however arrived at dark on April the 6th, in the nick of time. The two day battle, the costliest in American history up to that time, resulted in the defeat of the Confederate force and frustration of Johnston's plans to prevent the joining of the two Union armies in Tennessee. A total of 23,746 men were killed, wounded, or missing.