McClellan's plan initially was to utilize the James and York rivers, especially the former, which was known to be navigable to Richmond, in combination with his land-based forces, to attack simultaneously and overwhelm the unknown resources of the rebels at Richmond. However, even as several months were spent through the winter of 1862 training new troops and bringing these many Union assets into position, the portion of the scheme which depended upon control of the James River ran into trouble. In March, the Battle of Hampton Roads between the first ironclad warships took place. Although the conflict between the two ships was inconclusive, the new technologies were to change naval warfare dramatically, and control of the harbor of Hampton Roads was brought into serious question.