From one of my favorite sights.
http://nuclearweaponarchive.org/Russia/TsarBomba.htmlWe made some big badabooms too. We actually had 25 mt free fall bombs deployed and many in the 10 mt class as well.
http://nuclearweaponarchive.org/Usa/Weapons/Allbombs.htmlEven still, in 2009, we aren't exactly helpless.
http://nuclearweaponarchive.org/Usa/Weapons/Wpngall.html Look at the "total yield" numbers of the US enduring stockpile. Even our little cruise missiles can be dialed to blow at 150 kt, "almost 10x the yield of Hiroshima". We have 14 Ohio class SSBNs, down from 18, each one capable of launching 24 Trident D-5. Each D-5 missile capable of delivering up to 10 MIRVed warheads. Each warhead with a yield of 475 kt, "30x Hiroshima". And we can put each warhead into a ballpark from over 4,000 miles away, launched from a platform so silent even we cant find them.
We probably now have about 1/3 of the special weapons that we had in my day. Back then, '70s, it was the height of the Cold War and we had them, and delivery systems, all over the place. Most at a very high state of readiness and it would have taken only seconds and/or minutes for the entire thing to launch once we got the "go".