Lexington's protection keeps it in battlecruiser territory

What would the Lexington-class ships have been if the United States had completed them?

They can reasonably be called battlecruisers because their protection was not proof against their own main battery.

There is a strong case for classifying the unbuilt Lexingtons as battlecruisers rather than battleships. A compact test asks whether the armor belt can resist the ship's own main armament. One rule cannot capture every design nuance, but this one identifies the protection tradeoff at the center of the type. It also reinforces the need to read ship labels in their period design context.