I recall reading that the US flew F-111s up a particular valley very low at night, making use of their terrain following radar so the valley masked them from SAMs. the North Vietnamese apparently got cheesed off with this, and stuffed chaff into some dispensing mortar shells (flare bodies or such) and then one evening as the F-111 did their regular trip, filled the valley with mortar dispensed chaff up ahead of them, which the terrain following radar read as a cliff and ordered a quick pop-up into the clear air above. The SAMs and/or radar AAA got a shot off, and the F-111 drivers needed a change of underwear...
As for Japanese AA mortars - so did the British, the Holman Projector, a
pneumatic mortar no less.
https://en.wikipedia.org/wiki/Holman_Projector
A dozen or so kills, so not too bad for a lashed-up emergency contraption.