To make an opportunity of an input and an output of division in Bunker.
It is probable to make shooting from Bunker it will not turn out (restriction of opportunities Steel Panthers).
But it will be possible to be hidden from artillery impacts.
Characteristics of the bunker as it is usual, only to appropriate a class of transport that there was an opportunity load/unload divisions.
Are you talking about armed bunkers? Like the ones with guns and MGs?
You can give a carry capacity to bunkers just like transports, and there are things called "shelter bunkers" that serve just to hide troops (like HQ units). Look at units #205 and #206 in the Russian OOB.
Also, now that I look it up, all of the "Earthen Bunker" (with MGs) and "Concrete Bunker" (with antitank guns) units can already carry some troops.