The North Vietnamese had already sent units of their regular army into southern Vietnam beginning in late 1964. Some officials in Hanoi had favored an immediate invasion of the South, and a plan was developed to use PAVN units to split southern Vietnam in half through the Central Highlands. The two imported adversaries first faced one another during Operation "Silver Bayonet", better known as the Battle of the Ia Drang. During the savage fighting that took place, both sides learned important lessons. The North Vietnamese, began to adapt to the overwhelming American superiority in air mobility, supporting arms, and close air support by moving in as close as possible during confrontations, thereby negating the effects of the above.