On February 12, most of the Union troops departed Fort Henry, where they were waiting for the return of Union gunboats and the arrival of additional troops that would increase the Union forces to about 25,000 men. The Union forces proceeded about 5 miles (8 km) on the two main roads leading between the two forts. They were delayed most of the day by a cavalry screen commanded by Nathan Bedford Forrest. Forrest's troops, sent out by Buckner, spotted a detachment from McClernand's division and opened fire against them. A brief skirmish ensued until orders from Buckner arrived to fall back within the entrenchments. After this withdrawal of Forrest's cavalry, the Union troops moved closer to the Confederate defense line while trying to cover any possible Confederate escape routes. McClernand's division made up the right of Grant's army with C.F. Smith's division forming the left. USS "Carondelet" was the first gunboat to arrive up the river, and she promptly fired numerous shells into the fort, testing its defenses before retiring. Grant arrived on February 12 and established his headquarters near the left side of the front of the line, at the Widow Crisp's house.