Store the decryption key in a removable module or the wireless controller? Then anyone who captures one is stuck with a ball of encrypted code that can't execute. Dealing with securing software and keys against capture is not new for the military.
Also destroying the hdd/ssd is easier than destroying the whole machine. You could even have a secure wipe option if the machine is still able to run it's computer but is disabled mechanically.
Yup, I'm sure the countermeasures you can think of in the time required to write an HN post will be secure against technically-advanced nations' militaries.
Also destroying the hdd/ssd is easier than destroying the whole machine. You could even have a secure wipe option if the machine is still able to run it's computer but is disabled mechanically.