The Mark II Calculator is the World's Biggest Brain, Not the Fastest: May 1947
After the Mark I was unseated as the world's strongest computer by the Army's ENIAC, the Navy, looking to catch up, created the Mark II. The second generation improved on the Mark I in several ways, including a thinner and easier-changed roll of tape to spit out the answers, three more teletypewriters and calculations done entirely by electrical relays, without any of the Mark I's mechanical gears. Despite the Navy's best efforts, the ENIAC remained on top, 1,000 times faster than the Mark II.
Read the full story in Inside the Biggest Man-Made Brain