Seminole was a combined wepon design/effect test. The test device was exploded in a large water tank to
increase the shockwave to the ground. To some extent the test was simulating an underground nuclear detonation. The test
device was positioned in a circular chamber, wchich in turn was placed inside the water tank. The chamber still was
accessible by a corridor through the tank. Interestig point, the chamber was not exactly in the center of the tank,
to be precise - 10 feet off center. That led to a significant asymmetry in the resulting crater produced. The crater
was 660 feet wide and 32 feet deep.
The device was designed so that by the time when the fireball reached the tank walls the its growth would've been transformed from thermal radiation into hydrodynamic. Nevertheless the fireball was quite brigh as you can see on the pictures. In general Seminole was one of the most interesting (from visual standpoint) tests ever conducted.
And couple words about the nuclear device itself: The device used in the Seminole tyest was a bosted TX-28 primary/implosion system. It was 55 inches long, and 20 inches in diameter. Predicted predicted yield of 10 kt, actual yield 13.7. Total weight of the device was 1832 lb, the primary itself weighed 143.5 lb.