Physics detail: IR wavelength and glass

I believe I did mention sometime that normal glass isn't suitable for infrared sensors, and thus damage to such sensors' glass cover may be a huge spare parts problem in wartime.

This is indeed correct, and it's the reason why you can see with a thermal camera how well or badly your windows insulate a home thermally.

There are special glasses for IR sensors and other applications which require a high IR transmissivity, but they are not common and not used in armoured glass. It makes generally little sense to armour a transparent sensor cover, for (except in some freak version of polyurethane polycarbonate) stopped ballistic objects tend to cause enough damage to distort the vision unacceptably.

This kind of commander independent thermal viewer (rotatable IR sensor) on top of tanks may thus easily turn out to be largely useless in closed terrain, where all hostile infantry and stragglers take a harassing shot at it (if taught about this vulnerability):

The ability to cover the sensor with a movable bulletproof cover when it's not needed may help a lot (similar to the slotted window covers of old APCs and half-tracks), but the only real solution to the issue (and similar issues) is to have plenty spare parts (not only in depots, but also in the unit and the vehicle). The ability to replace a damaged window quickly or even under armour protection (as it's done with the panoramic view mirror modules or the cupolas and driver position) would be very useful.

This applies as well to the new kind of APC, which uses large windows (due to improvements in armoured composite glasses) instead of the traditional panoramic mirrors for the driver and other crew members/passengers. This approach is popular for MRAPs, blue helmet APCs and generally APCs not meant for the thickest of fights.

Windows are similar to tires; vulnerable to bullets and in need of a good spare parts reserve and supply.

This is an example of the not-totally-obvious issues* an armed bureaucracy faces if it serves the public. 

The bureaucracy's self-interest isn't in building up large stocks of spares, particularly not if no previous painful experience has pointed out the need for this (because of the spare being part of an innovation). War reserve stocks of ammunitions are painfully low and were painfully low in many countries (the Soviets/Russians addressed this by keeping ancient ammunition in stock until they sold out to client states, with respective dud rates).

This identifies a spot where the self-interest doesn't necessarily push the bureaucracy into doing the right thing, and hence this spot would be a good one for civilian oversight. Methods of oversight may include freedom of information requests (which might be answered on such topics at least in some countries) and similar more powerful parliamentary requests for information.
You may end up having a gazillion bucks military failing to do its trick for more than four days if no such oversight is forced on it.


*: Similar to the discarding sabot issue with IFV autocannons which I mentioned earlier and the unprotected and thus often-perforated bore evacuators on M1A2 Abrams tanks in 2003/2004.

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