Hedgehog and Squid grew from prewar ASW work

Were Hedgehog and Squid invented before the war or during wartime development?

They grew from mid-1930s work and were accelerated by wartime need, with details shared once the Royal Navy was satisfied.

Hedgehog and Squid were not sudden wartime inventions. Work had begun before the war, and the systems might otherwise have matured later. The Battle of the Atlantic forced rapid development, and the Royal Navy shared details with the US Navy once it was satisfied with them.