Years and years ago, according to the legend, a mother dipped her boy called Achilles into the River Styx. This made him impenetrable to any swords or arrows at the time. She held him in the river by the heel, which is where a bloke called Paris shot him; fatally.
You can cover a remote fighting vehicle with armour but somewhere there is a point where the communication signal has to go in.
Track that and you have got it.