Zumwalt's hull form and the 1980s stealth studies

How long had the United States been studying the hull form associated with Zumwalt?

The relevant hull-form and stealth-destroyer studies are dated to the 1980s in this discussion.

Study of the hull forms associated with Zumwalt is traced to the 1980s, slightly after the beginnings of the Burke programme. Stealth-ship and stealth-destroyer concepts from that period already explored comparable shapes. That gives the modern ship a longer design history than its construction date suggests. Similar shapes can also emerge through convergent development, so visual resemblance alone does not establish copying.