W38

By shaping the plutonium pit into an ovoid [like a small watermelon, smaller than a football], Livermore weapons designers were able to dramatically reduce the size and number of explosives needed to detonate the bomb. The The W47 was the first warhead in this new generation of weapons. Although it was only half as large as the bomb that leveled Hiroshima, but it had 80 times the yield.

The Livermore-designed W38, W45, and W47 share a common primary, the "Robin."