@parker I believe the software for fire control and targeting systems is proprietary and the copyright and source code holder is either the US military or some contractor, but really the contract of such tank purchase should have required that the source code be included under a free license.

Software doesn't necessarily need to be published under some version of GPL to be free.

It would be a major violation of the tank purchasers freedom for the tank to run proprietary software, but whatever insurgents do appears to be unrelated, as they never end up owning the tank - they only operate it.