In the summer of 1954, shortly after the 15 megaton Castle Bravo nuclear explosion contaminated hundreds of miles of the Pacific Ocean and the Marshall Islands, Edward Teller, the "father of the H-bomb," proposed a new weapon known as the SUNDIAL. The only real detail about it that has been released was its explosive yield: 10,000 megatons. Which is to say, 10 gigatons.
When Teller briefed an advisory board of government scientists on it, they were horrified:
Dr. Fisk said he felt the Committee could endorse [Livermore's] small weapon program. He was concerned, however, about Dr. Teller's 10,000 MT gadget and wondered what fraction of the Laboratory's effort was being expended on the Gnomon and Sundial. Mr. Whitman had been shocked by the thought of a 10,000 MT [bomb]; it would contaminate the earth.
A congressional committee was secretly briefed on it. This exchange is rather wonderful:
SENATOR JACKSON: This is a design that will end once and for all Malthus' theory of population.
DR. BRADBURY: You don't have to deliver it — just leave it in your backyard.
To put it into perspective, the largest bomb ever detonated, the Tsar Bomba, could at its maximum yield have been 100 megatons (100,000 kilotons). The bomb detonated on Nagasaki was 20 kilotons; the largest bomb the US ever detonated, Castle Bravo, was 15 megatons (15,000 kilotons). The SUNDIAL would have been 10,000 megatons (10,000,000 kilotons), one hundred times more powerful than the Tsar Bomba, 500,000 times more powerful than the Nagasaki bomb. It could scorch an area the size of France or Texas.
The program was axed by the Eisenhower Air Force, who concluded they had no military need for such a weapon, which looked more like a "doomsday device" than something they could actually imagine using. I find it quite interesting (as someone who researches this stuff) that this was just a little too "on the nose" for them — a scientists' fascination, but not one that would work with a military doctrine that believed (rightly or wrongly) that nuclear war could be fought and won.
TLDR;: US weapons scientists actually did consider building Dr. Strangelove-like contamination weapons of humongous proportions.
Source: my blog 🙂
Added a few links to screenshots of the documents, for the suspicious. I work on this kind of thing for a living. It's a fun job if you can get it…