RDS-37 was the Soviet Union's first "true" (staged) hydrogen bomb, first tested on November 22, 1955. The weapon had a nominal yield of approximately 3 megatons. It was scaled down to 1.6 megatons for the live test.
It was a multi-stage thermonuclear device which utilized radiation implosion called Sakharovs "Third Idea" in the USSR (the Teller–Ulam design in the USA). It utilized a dry lithium deuteride fusion fuel, with some of it replaced with a "passive material" to reduce its total yield. Despite this reduction in yield, because the weapon exploded under an inversion layer much of its shock wave was focused backward at the ground unexpectedly, causing a site building to collapse and kill three people.
It was air-dropped at Semipalatinsk Test Site, Kazakhstan, making it the first air-dropped two-stage thermonuclear test. The RDS-6s device (Joe-4) exploded in 1953 was labeled as a "hydrogen bomb" as well but was more similar to a "boosted" fission bomb than a megaton range hydrogen bomb.