Richard Rhodes (1995). « chapter 13 ». Dark Sun: The Making of the Hydrogen Bomb. p. 251. 

« The first problem assigned to the first working electronic digital computer in the world was the hydrogen bomb. […] The ENIAC ran a first rough version of the thermonuclear calculations for six weeks in December 1945 and January 1946.

Although ENIAC was designed and primarily used to calculate artillery firing tables for the United States Army’s Ballistic Research Laboratory (which later became a part of the Army Research Laboratory), its first program was a study of the feasibility of the thermonuclear weapon.

ENIAC was completed in 1945 and first put to work for practical purposes on December 10, 1945.^[10]

ENIAC was formally dedicated at the University of Pennsylvania on February 15, 1946 and was heralded as a « Giant Brain » by the press

One of the earliest digital computers was brought online on February 14^th, 1946, when the University of Pennsylvania announced the “Electronic Numerical Integrator and Computer”: ENIAC. Constructed at the Moore School of Electrical Engineering, ENIAC was built for the purpose of calculating artillery-firing tables, which provided information to help artillerymen aim their weapons. ENIAC weighed more than 60,000 pounds, covered 1800 square feet of area, consumed 150 kilowatts of power, and cost $500,000 to build (about $6,000,000 in today’s dollars).

For their money, the U.S. Army Ordinance Corps received a processor that could handle 50,000 instructions per second. ENIAC did significantly speed up calculation times—artillery calculations that had previously taken twelve hours on a hand calculator could be done in just thirty seconds. ENIAC was intertwined with nuclear science from the beginning: one of its first real uses was by Edward Teller, who used the machine in his early work on nuclear fusion reactions.

https://www.atomicheritage.org/history/computing-and-manhattan-project