Plans to use five thermonuclear explosions to create an artificial harbor at Cape Thompson, Alaska, for Project Chariot in 1958. It was eventually cancelled amid controversy and protest. The outer-outline represents the "full scale" plan, which would require detonations totalling 2.4 megatons. The inner outline is a scaled down version, of 460 kilotons. It would be eventually scaled down to 280 kilotons.
Source: Scanned from Dan O'Neill, The Firecracker Boys (New York: St. Martin's Press, 1994).