Does the selling country install software/hardware into the weapon that could be accessed by the selling country to make the weapon inoperable in case of war with the purchasing country?
I would think that this would be:
strategically sound from a national security perspective, but
not be a feature the buying country would want, however
be practically impossible to detect by the country who purchased the weapons until it was too late.
For example, say country X sells country Y some state of the art jet fighters. Would it not be easy to imbed something inside the fighters to keep them from, let’s say firing up the engines, from a remote location?
But it is known that countries that sell weapons generally protect sensitive bits with what is known as anti tamper features. That is so the receiving country cannot take some sensitive technology apart, reverse engineer it, and sell it to others.
One google search term you will find helpful is ‘Russian Monkey Model’, most countries don’t sell the top of the line, and if they do they’re crippled export versions.
I have some expertise in this field and can (in general, no specifics), address it.
I know of no “on-off” switch as the OP mentions. However, systems that are considered sensitive are often ‘downgraded’ to remove the most sensitive components and replace them with something else perhaps slightly less efficient. And the codes to change settings in the threat ID (where a country could make US systems to be seen as a threat) are never given out, even to our most staunch allies, to the best of my knowledge.
What they do get depends on the country, the political landscape, and what they can afford; some weapon systems we’ve sold have probably been as good if not slightly better than what the US Forces have.
The difference is who controls the maintenance, the support, the training, the spare parts…and that’s us (or any other country dealing weapons to other countries).
The weapons are produced by arms companies and the government decides which weapons to sell or what changes need to be made to them.
However, like everything else for the right amount of money some people would sell their mothers soul and there is usually somebody in the company to sell it.
Since the US will not supply the source code that comes with its advanced exports, I would take it as given that some back door shennanigans can be possible. But that would be a one time only and it would have to be for all the marbles.
Boeing wouldn’t supply Britain with the source code for the avionics software in the Chinook HC3s it bought, which meant they were not cleared to fly in anything but bright sunny cloudless weather.
My company participates in Foreign Military Sales of equipment, and we specialize in GPS, which is downgraded to not allow use of the encrypted military P(Y) code, and in the future, the so-called M-Code. These allied militaries are using the same C/A code you use in your phone, which is only accurate to about 100 feet. That’s good enough for basic navigation, but not for targeting. Mission computers and avionics suites are often downgraded as well on military aircraft. That’s not to say the host country can’t still build and install their own that may be equal or better. My understanding is that Israel is well known for doing that. It will be interesting to see what changes are made to the Joint Strike Fighter (F-35) since we are selling that to our allies at almost the same time they are being provided to our own troops.