Planetary invasions, Tech "smuggling"

Advanced sensor suites may not be as much help as you might think. For
instance, in Dean McLaughlin's "Hawk Among the Sparrows" we have a TL7
or 8 fighter/recon plane against TL 5(?) biplanes (think of an advanced
version of the SR-71 getting thrown back to WW I).

The pilot discovers to his horror, that his radar & heat guided
missiles are useless. There's so little metal in the biplanes that the
radar rejects them as static or decoys. And as for heat seeking, there
are several orders of magnitude difference between a jet turbine and a
primitive internal combustion engine.

As for guerillas needing to hide weapons, it all depends. What you can
do with common household items is astonishing. If you allow "safe"
industrial items the list grows even more. A certain type of fuel and a
certain agricultural chemical combine to make an explosive rather
better than dynamite, if somewhat less stable.  This is why the Army
has *long* lists of materials that must be controlled if sabotage or
guerilla warfare are expected.

BTW, a trebuchet makes a nice, hard to detect, indirect fire artillery
piece. It's got quite a range if you are using high TL projectiles.

Now as to getting things past TL restrictions, allow me to suggest
reading "King David's Spaceship" by Jerry Pournelle. To someone at
TL14, the difference between TL3 & TL4 may be insignificant. To the
mercenaries on the ground, it is *quite* a difference.

Also, given the benefit of a few extra TLs of knowledge, you can do
some amazing things at the low TLs. I and a friend once drove a GM
nuts. He'd dropped "us" complete with our knowledge into a fantasy
medieval world. In short order we were raking in lots of cash with
things buildable with our knowledge, but that TLs tools. Even with
medieval "chemistry", things like nerve gas are possible, if you know
some *real* chemistry.

I strongly suspect that some players with a pocket computer containing
the imperial encyclopedia and some reference works could make
themselves indispensible on a low TL worldm. And with a bit of luck,
make it low like "native" breakthroughs.