The Department of Defense in a report on “Open Technology Development” (PDF), on the importance of software to the military:
Software is the fabric that enables modern planning, weapons and logistics systems to function. It might be the only infinitely renewable military resource. Capabilities evolve as new software is created anew or builds on existing software. From ground sensors to satellites, software is pervasive; it is the final expression of military knowledge transformed into source code and deployed on the battlefield.
The report also provides an apt analogy for closed, proprietary software:
Imagine if only the manufacturer of a rifle were allowed to clean, fix, modify or upgrade that rifle.