No 4. Test No. 6 3,300 Kilotons
This was the first Chinese staged thermonuclear test. It was a fully-functional, full-scale, two-stage hydrogen bomb which was tested after 32 months of testing the first fission device by China. This credited China with the shortest fission-to-fusion development in history.
No 3. Ivy Mike – 10,400 Kilotons
Detonated on Enewetak atoll, Ivy Mike was the first United States nuclear test of a fusion device. It is considered to be the first successful hydrogen bomb test in history. The fireball from the explosion was approximately 5.2 km wide and the mushroom cloud rose to an altitude 17.0 km in less than 90 seconds!