When the Electronic Numeric Integrator and Computer (ENIAC) was developed for the purpose of calculating the ballistic trajectories human computers like Bartik had been doing by hand, she applied to become a part of the project and was eventually selected to be one of its first programmers. Bartik was asked to set up problems for the ENIAC without being taught any techniques. Six women, including Jean Jennings Bartik, Betty Holberton, Marlyn Wescoff, Kathleen McNulty, Ruth Teitelbaum, and Frances Spence, were chosen to be the main programmers for the ENIAC. Many other women who are often unrecognized contributed to the ENIAC during a period of wartime male labor shortage. Bartik, who became the co-lead programmer (with Betty Holberton), and the other four original programmers became extremely adept at running the ENIAC; with no manual to rely on, the group reviewed diagrams of the device, interviewed the engineers who had built it, and used this information to teach themselves the skills they needed. Initially, they were not allowed to see the ENIAC's hardware at all since it was still classified and they had not received security clearance; they had to learn how to program the machine solely through studying schematic diagrams. The six-woman team was also not initially given space to work together, so they found places to work where they could, in abandoned classrooms and fraternity houses.