Which of the following was an early computer used for military purposes?

ENIAC, or Electronic Numerical Integrator and Computer, holds historical significance as one of the first general-purpose electronic digital computers. It was developed during World War II and primarily used for military applications, particularly in calculating artillery firing tables for the United States Army. ENIAC's ability to perform complex calculations at unprecedented speeds laid the foundation for future advancements in computing and greatly influenced both military and civilian applications.

Colossus, while also an early computer used in a military context, focused specifically on code-breaking during World War II rather than being a general-purpose computer. UNIVAC, the first commercial computer, was designed for business use and general purposes, not specifically military. The Apple I was a personal computer that was developed long after the early military computers and was intended for individual consumers rather than military applications. Thus, ENIAC is recognized as the correct answer due to its role in military operations along with its pioneering computing capabilities.