Single Use units are a type of diverse units available. These units, as the name implies, can be used only a single time, and are lost after the battle ends, win or lose.
The main advantages of single-use units are that they are extremely inexpensive, and can also be purchased during enemy turns, if they attack you.
When using single-use units, make sure to place them in good positions in deployment, as they cannot be moved (with the exception of light infantry) during a battle. Also, make sure you take advantage of the abilities of your unit, as it is nearly pointless to use Air Defence Towers against tanks, or Bunkers against air units, for example.