All internal evaluation units of public sector agencies face tradeoffs arising from the tension within the "independence-accountability-learning" nexus. Most such units are not independent, unlike the World Bank unit, which was ostensibly independent from its inception half a century ago. But new archival evidence reveals that between July 1973 and October 1974 President Robert S. McNamara and other principals resisted independence--which entailed the transfer of evaluation governance from management to the shareholders. This effort was in vain because the United States government used its leverage over the World Bank to impose the General Accounting Office's preferred model of independent evaluation. The debate in the early 1970s about whether independence would result in isolation, thereby hampering learning by operations staff, still resonates. Recent external reviews have concluded that accountability tends to trump learning in World Bank evaluation, suggesting lessons for internal evaluation units more generally.