Vietnam in December 1965 after the Battle of Ia Drang. He "concluded that it had not been a victory at all and that Westmoreland's big-unit strategy was misconceived". However, Johnson publicly said there was no alternative to disrupting enemy main force units in the Central Highlands as preventing them from establishing base areas in the middle of the country was essential. After talking to junior officers involved in the first major actions, Johnson concluded that enemy main force units had the ability to evade engagements, giving them the option to keep casualties below an acceptable level, but they were in fact accepting the actual kill ratios being achieved, as evidenced by them attacking United States forces. Johnson started the process to have Westmoreland replaced in Vietnam, and commissioned the PROVN Study, which noted that "aerial attacks and artillery fire, applied indiscriminately, also have exacted a toll on village allegiance." There was a deep-seated reluctance among the Joint Chiefs of Staff to interfere with the command decisions of Westmoreland, but harassing artillery fire, by United States forces at least, was greatly reduced. As Johnson saw it, the communist units would always keep their casualties below what they considered a prohibitive level, and could not be swept away by US firepower. He did, however, acknowledge that the U.S. Commander in Vietnam, General William Westmoreland, had little choice but to engage the enemy's main formations, which had to be prevented from securing base areas where they could concentrate. Johnson was instrumental in altering the focus to a counterinsurgency approach, but was frustrated at the US Congress' refusal to provide the manpower necessary for successful pacification. In his later years Johnson said it had been obvious that US national mobilization was required to win in Vietnam, and he regretted not resigning in protest at the government asking the army to fight a war without hope of ultimate victory. Conditions for enlisted personnel As Chief of Staff, one of Johnson's noteworthy accomplishments was creating the office of the Sergeant Major of the Army to improve the quality of life for enlisted personnel. He selected Sergeant Major William O. Wooldridge to be the first to hold this post. Johnson also served as acting Chairman of the Joint Chiefs of Staff for a few months in 1967 during the convalescence of General Earle Wheeler. Johnson retired from active duty in July 1968. For three years, General Johnson