Electrical / electronics.
The common electrical system in standard vehicles sometimes needs to be modified, upgraded or simply is not just enough. In special, in military applications not only there are strict standards to be met, but also there are some tactical reasons that makes the military electrical systems really complex in special if civilian lighting systems must coexist with the blackout military ones or make living together 12v and 24v systems in the same vehicle.
The electronic devices must be tropicalized and mecanically improved in order to make them resistant to abusive use in extreme conditions as vibrations, water inmersion or high temperatures beyond the civilian vehicles.
InTT Automotive has a valuable experience in such kind of applications and has militarized several civilian models for military applications as prototypes for the army.