Garrison strength

by damage output

what do you mean by damage output ? Militia L-1= 3 when defending L-2= 5.5 when defending ?

while attacking

It has something to do with the largest D value, or the sum of all D values, modified by terrain bonuses.

The reason I think this is because AT guns and infantry have higher garrison values than medium tanks. The MT is a much more powerful unit most respects. But AT guns have high D. So does infantry. Especially in a city. An AA gun can garrison a hills province on its own, even though it's a weak unit in most respects, but it has a high AA defense, especially in hills.

By the way, this may be the best use of starting AA guns in the early game. They are useless for attacking infantry, but they are decent garrison units.

thank you for the information