The nineteenth century's largest naval missed opportunities

What was the biggest nineteenth-century naval missed opportunity outside the Royal Navy?

The nominations are the United States losing the momentum of its Civil War naval expansion and France pursuing the Jeune École, with a broader warning about drawing sweeping lessons from unusual battles.

One nomination is the American failure to maintain the naval momentum created during the Civil War. Although much of that expansion served coastal and river warfare, it had also produced technology and operational experience that could have supported further development. The French Jeune École receives a separate, strongly critical assessment as a doctrine that undermined the navy's opportunities. A more general caution concerns lessons drawn from the century's infrequent battles, which often occurred in unusual circumstances. The judgments focus on what navies retained from earlier experience and how confidently they interpreted limited evidence.