Each side's War Minister, Prime Minister, and Monarch are authorized to transfer men and batteries between that side's units. The CO or XO of the unit that is giving up the men or batteries may also submit a transfer order for his unit.
Infantry units may not be raised above 1500 men and one battery, nor below 501 men. Cavalry units may not be raised above 1000 men and one battery, nor below 501 men. Artillery may not be raised above 300 men and 3 batteries, nor below 200 men and 2 batteries. Militia units may not be raised above 1000 men nor below 501, and may not have batteries. If a transfer order would violate these limits, the order is not carried out. Headquarters units may not transfer men at all. (In unusual cases, ask the GA for a manual intervention.)