(Reuters) Turkey says Russian S-400 defense system purchase done deal. There is a purely technical reason why Turkey’s purchase should hard-block even limited acquisition of the F-35.

Stealth is both a system and a game. By operating both the F-35 and the S-400, the S-400 operator radar operators obtain unlimited test data on the stealth characteristics of the plane. The mass of data so acquired would exceed by a great margin normal exposure of the F-35 to adversary systems.

With this massive, artificial exposure, it could be possible to game the F-35, compromising its stealth defenses, destroying, for all the operators, billions of dollars of cumulative investment. Most of the stealth characteristics of the plane are in the geometry of the airframe. But the plane has other tricks as well, far too valuable to expose to Russian equipment.

The Turks could argue that they are trustworthy. But since the S-400 computers are Russian, they could  come with preinstalled, undetectable “malware” that eases transmission of F-35 data back to the Russians. It doesn’t have to be something as sneaky as a burst transmitter, although it’s interesting to consider how a data burst could be disguised in a radar pulse. It could be  as simple as  prepackaged data in a background process, preserved in unallocated memory for quick dump to a USB memory stick.

Rigorously considered, this is not a  foreign policy issue. It is a technical one, which mandates denial of the F-35 to Turkey.  Relations with Turkey cannot be allowed to intervene.

Let’s not spill these hard-won F-35 beans.