The first major battle between the United States Army and the Peoples’ Army of North Vietnam, the battle of the Ia (River) Drang in the Central Highlands of South Vietnam, involved approximately 2500 North Vietnamese troops, the 66th and 33rd regiments, opposing 1,000 troopers of the 1rst Cavalry division. The American attack on these two regiments was part of the Pleiku campaign from October 26, 1965-November 25, 1965 which ended with the destruction of the three regiment North Vietnamese force occupying the Chu Pong-Ia Drang complex.
The attack of the 1rst and 2nd battalions of the 7th Cavalry and the 1rst battalion of the 5th Cavalry demonstrated the speed with which American units could be transported by air, and the firepower from air support that the Americans had at their disposal. On the other hand the Americans were taken aback at the ferocity of North Vietnamese counterattacks, and the ability of the North Vietnamese to isolate American units and subject them to withering fire power. Ultimately the battle demonstrated the futility of the North Vietnamese engaging in a stand up fight with the Americans, and giving the Americans time to call on their formidable array of support fire. North Vietnamese KIAs of around 2000 were ten times the KIAs sustained by the Americans. Half of the American casualties were caused by an ambush of the 2nd battalion of the 7th cavalry at landing zone Albany on November 17th which lasted for sixteen hours.
The battle foreshadowed aspects of the war: American mobility, American firepower, the ability of the North Vietnamese to break contact and vanish when a battle was going against them and the ever present danger to American forces of ambushes. American units could inflict far more casualties than they received, but ultimately over eight years the death toll of Americans reached 58,000 and the American people were unwilling to continue paying the cost. Go here to read the after-action report of Hal Moore who commanded the 1rst battalion of the 7th Cavalry.