I hope my title is at least mildly provocative and gets you to read the Snopes debunking:
https://www.snopes.com/fact-check/metric-system-pirates/

We have all heard the story that the US would have been metric from the beginning if pirates hadn't stolen the meter and kilogram samples sent from France and killed the man accompanying them. Not true, says Snopes. Please read the arrrrrhticle, but a couple of snippets for flavor:

Jefferson's report is widely considered by historians to be a foundational and important document in the history of unit standardization in America. That said, it did not lead to any policy, nor did it spur legislation. The report was essentially filed away for a later Congress to deal with. 

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The problem with moving forward on any plan, according to the National Archives, was congressional inaction and a confusing mix of competing proposals. Despite repeated instructions by Washington and several later presidents to get the job done, nothing actionable was signed into law until the 1820s and '30s. . . . .

While it was true that physical items to demonstrate metric standards intended for Jefferson did not make it to him because of piracy, there was no plausible alternative history in which the delivery of such items would have overcome the political stalemate over establishing a standardized measuring system — no matter if it was the decimal-based metric system or something else.

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