 He established a supply base on the Pamunkey River (a navigable tributary of the York River) at White House Landing where the Richmond and York River Railroad extending to Richmond crossed, and commandeered the railroad, transporting steam locomotives and rolling stock to the site by barge.On May 31, as McClellan planned an assault, his army was surprised by a Confederate attack.Johnston saw that the Union army was split in half by the rain-swollen Chickahominy River and hoped to defeat it in detail at Seven Pines and Fair Oaks.