The primary bad guy in the Terminator films is not any of the machines sent back in time to destroy the Resistance before it can even begin, but the sentient computer that controls the machines – Skynet.
In Terminator 2, we learn that Skynet is, effectively, its own creator. The T-800 sent back to 1984 to kill Sarah Connor may have failed in its mission, but the computer chip that was its ‘brain’ and an arm are salvaged by a robotics firm called Cyberdyne, that begin to study the chip. The advanced technology doesn’t function, but it pushes the developers at Cyberdyne in new directions, encourages them to explore new ideas, and the end result is Skynet – a military supercomputer that, upon going online, learns, as the T-800 in T2 describes it, at a ‘geometric rate’.
The result of this is that Skynet, on the 29th of August 1997 in the original chain of events, becomes self-aware. It immediately determines humans are its enemy, and launches America’s nuclear weapons at Russia. Russia, naturally, responses in kind, resulting in mutually assured destruction and three billion human casualties.
The survivors have to deal not only with the destruction of much infrastructure, but the rise of an army of machines bent on wiping humanity out, once and for all. Skynet builds a variety of Terminators and Hunter Killers to achieve its goal.
Aerial Forces
(An aerial Hunter Killer fires its plasma cannon)
Skynet patrols the skies via aircraft-sized Hunter Killers, armed with plasma cannons. In Terminator Salvation, we see these things dogfight quite effectively against A-10 aircraft, and they appear quite agile. They can be felled by surface-to-air rocket launchers, and the missiles of an A-10 can also destroy them.
A small drone is also seen in Salvation, that appears to be unarmed and operates to scout targets.
Ground Forces
Skynet possesses large ‘tanks’ with both twin-turret and single-turret varieties.
(a HK tank is destroyed by a pair of grenades thrown under its tracks)
In T1, one of these blasts a person apart, and they demonstrate rapid fire and quick target acquisition. They might have weak underbellies, since a pair of grenades that detonate under one of its tracks completely destroy it.
Skynet also uses T-600s (seen in Salvation) and T-800s as infantry, and has some form of armed motorbike. There are also eel-like machines that swim in lakes and rivers, waiting for unsuspecting humans.
Is Skynet hardware or software?
Skynet is said to be software in T3, having infected the internet and spread its tentacles across the web. This makes sense – it was about to launch nuclear attacks against major cities, which would also constitute major hubs of internet activity, as well as large-scale computer facilities. Destroying those facilities would inevitably destroy Skynet if it didn’t move into other systems.
As the Future War raged, Skynet may have needed to withdraw itself from these systems and to more centralised hubs, away from potential human interference. In turn though, this would leave Skynet vulnerable to large-scale attacks. However, given Resistance encroachment upon Skynet positions and ultimately, the successful destruction of Skynet’s defence grid (referred to in T1), it seems that Skynet did indeed centralise its operations.
Could it happen?
Currently, we are very far away from developing a sentient computer system of any kind, and whilst we can build robots, they are nothing like the ones in the Terminator films. It’s conceivable that in time, we might be able to build such machines, but I am not confident that will happen in my lifetime.
When we do, will a sentient computer or robot be favourable to humankind, or will it consider us to be an enemy? I have no answer to that.