The first thing we did?

It was 4 years later and the US did not even have nukes when attacked.

Does developing nukes count as a thing, how about the Doolittle raid, Iwo Jima?

Unrestricted submarine warfare, Island hopping, the Solomon Islands, Guadalcanal, Tarawa, Marianas, Coral Sea, Midway, the Aleutian Islands, the liberation of the Philippines, Okinawa?

So maybe not the first thing!

Edit :- "Nobody threatens to nuke somebody if they’re going to nuke somebody."

Wasn't the entire doctrine of "Mutually Assured Destruction" based on this very idea, the implicit threat of a nuclear strike given certain red lines?

The first thing we did?

It was 4 years later and the US did not even have nukes when attacked.

Does developing nukes count as a thing, how about the Doolittle raid, Iwo Jima?

Unrestricted submarine warfare, Island hopping, the Solomon Islands, Guadalcanal, Tarawa, Marianas, Coral Sea, Midway, the Aleutian Islands, the liberation of the Philippines, Okinawa?

So maybe not the first thing!

The first thing we did?

It was 4 years later and the US did not even have nukes when attacked.

Does developing nukes count as a thing, how about the Doolittle raid, Iwo Jima?

Unrestricted submarine warfare, island hopping, Guadalcanal,Tarawa, Marianas, Coral Sea, Midway Aleutian Islands, The liberation of the Philippines, Okinawa?

So maybe not the first thing!