Transatlantic shipbuilding networks made G3 secrecy porous

What did the US Navy know about the supposedly secret G3 battlecruisers?

Enough to understand their power, because the British and American shipbuilding industries shared personnel and information extensively.

Thousands of people would have worked on the G3s, so their capabilities were never confined to a tiny circle. American citizens held senior technical positions in British yards while British naval architects worked in American industry. Engineers also exchanged information through professional and social networks, continuing cooperation established during the First World War. Washington might lack every official drawing. Shipyard knowledge and ordinary professional conversation were enough to reveal the scale and purpose of the British ships.