This is just an idea, i do not intend to make it into a whole Story.
The Planets name said it all: Djungle
It was mostly covered in a dense, rainy rainforrest, and a few small oceans.most of the time it rained on Djungle.
But the inhabitants were used to that, what was more of a problem was that Djungle was in a strategically important position. One can imagine that a planet in a strategically important position is interesting, and changes ownership frequently.
Sometimes the people of Djungle were fed up and tried to gain control for themselves, but usually that was not very successfull.
This time, they reconed, we need a new aproach. so they sat together and discussed their options, wich they did not have too many of.
Whenever they had tried to get rid of the ocupants they had failed miserably, because the warmachines used against them would detect anything with a fusion reactor, anything that radiated heat, like ICE-engines, and even anything that was made from metal. Infantry was not easyly detected because the planet was to warm to allow for a good contrast against the surrounding air, and so were animals(read: horses(cavalry)) but as soon as anything with a large barrel fired the hot barrel would be clearly visible even from a satelite.
once they had even used a few long-toms, but the ASFs has quickly disposed of them, leaving a useless stockpile of granades.
so what options did they have? infantry? cavalry?not really usefull against a modern days warmachine.
mines? anything metallic in the mechs path would have been detected, and they did not have the idea for non-metallic mines.
so they were clueless until one conspiracists son, when he served tea to them said one word:
What do you say?
Well: we have grenades that do a lot of damage, we just have to hurl them at the enemys from some distance.
a trebuchet is made from wood, it uses a counterweight to throw stones at a target that could be 300 metres away, unlike a cannon it does not use chemical energy so it won`t get hot. the only way to see it in heavy rain is Mk1 eyeball. to move it in place horses could be used, and instead of stones we hurl those Long-tom grenades at them. They might get the idea what hit them, but not where it came from. they will search everywhere and will scan most of the planet for a hot gun-barrel by satelite, but they will not see the trebuchet hiding in the forrest nearby.
and so the trebuchet-rebellion started.
typos and spelling-mistakes are property of the finder. english is not my mother-tongue.