Sim HQ explans this on their forum for the game. <a href="http://simhq.com/forum/ubbthreads.php/topics/3761010/Can_someone_explain_how_the_op#Post3761010">http://simhq.com/forum/ubbthreads.php/topics/3761010/Can_someone_explain_how_the_op#Post3761010</a> Supply units will supply units in the adjacent grid squares during the beginning of the operations phase and during this this time(operations phase)you should be able to click on units and allot ammo to your squads.There is a limit to how much each supply