Snowball is the main leader of the animals' military defense in the Battle of the Cowshed. This happens in Chapter 4.
In this chapter, we see that Snowball has learned a lot about leading military operations. He apparently learned all of this from reading some old books about Julius Caesar's military campaigns. He puts the information to good use. He tells all the animals where to be as the battle is about to start. And he is the one who orders the animals to attack when the time is right and when to pretend to retreat so as to trick the humans.
Snowball's strategic prowess mirrors his Russian Revolution counterparts quite effectively. Trotsy was an incredibly strategic military leader who got the job done under Lenin as he was supposed to.
Likewise, Snowball's effectiveness earned him an honor among the animals: "Animal Hero, First Class." He also gave an inspirational speech that moved and motivated the animals. He spoke of the need for all animals to be willing to die for Animal Farm. At this point, Snowball appears an appropriate fulltime leader for the animals.
Snowball and some of the other animals anticipated that Jones and his men might try to take back the farm. In preparation for such an event Snowball had studied books on Julius Caesar's battle tactics and put himself in charge of defending the farm. Snowball put the animals into place for the attack. When the men came Snowball directed the attack and when he could he, himself, charged Jones taking a bullet to his back which grazed him and left him bloody, but the farm victorious over Jones. Napoleon is not even mentioned in the Battle of Cowshed once, but later after Snowball has been run off he tries to convince the farm, quite successfully, that it was he who was wounded during battle and heroic and that Snowball had helped Jones plan the attack.