Why G3 and N3 responses could not begin immediately

How quickly could the United States or Japan design and build an answer to Britain's G3 and N3 capital ships?

Their occupied slipways and existing building programs meant that even starting a response would take at least two to four years, with Japan probably taking longer.

American and Japanese yards were already committed when the G3 and N3 challenge appeared. They would have to finish or cancel current ships before clearing slipways for a new class. The estimate is at least two to four years before construction of a response could begin, with Japan likely taking longer. Industrial scheduling is the first constraint on an apparently simple design competition.