Operation Greenhouse was a series of nuclear tests conducted at
Eniwetok Atoll in early 1951 to test various design principles that would later
become pivotal in the development of thermonuclear weapons. The purpose of
these tests was to reduce the size, weight, and amount of fissile material
necessary for nuclear weapons, while simultaneously increasing their
destructive power.*
Source:
*http://www.atomicheritage.org/history/hydrogen-bomb-1950