Brett Butler

I'm have arma 3 and the apex dlc and a few other dlc content. I'm trying to just get in the artillery tanks and It wont let me at all. I'm getting very frustrated and want to be able to use everything. is there a mod I need or is it something such as a different class. I have been in maps with thprimary artillery and secondary and either wont let me get in the m4 or anything else to drive or shoot them. any advice would be greatly appreciated!