No wizard chose to take a cannonball head-on with the Shield Charm.
This was a lesson bought with the blood and tears of their comrades.
Rifles and pistols were manageable; the Shield Charm could easily block them.
If the shell was fired by a Squib—nothing more than a huge lump of iron without the slightest magical fluctuation—
that was no problem either.
A full-fledged Auror's Shield Charm was enough to withstand a solid iron cannonball.
But cannonballs exploded!
The violent blast alone was enough to knock a wizard unconscious, or even kill them on the spot.
So, Apparating away was the first choice.
But with Grindelwald here, would he let the wizards present Apparate so easily?
Obviously not. After several wizards were splinched while Apparating, they told everyone that Apparating now was suicide.
Thus, aside from dodging, they had no choice but to take the shells head-on.
And when it came to dealing with cannonballs directly, there was no magic more useful than Transfiguration.
Take the Exploding Charm, for instance. One shell was fine, but the sparks from the blast were enough to keep you from seeing whether a second one was following close behind!
With Transfiguration, cannonballs could be turned into paper, pinewood, butterflies, little birds...
But there was a problem! Ordinary Transfiguration required the spell to hit the cannonball!
Moreover, a single-target spell could hardly account for everything around them.
This was when teamwork was put to the test.
The wizards hurried to their respective squad leaders.
They cast magic together, forming a thin barrier overhead across the area they occupied.
Any cannonball could easily punch through this barrier.
Yet the solid, gleaming shells turned into metal powder and gunpowder powder after passing through it.
This was the most basic application of Transfiguration—altering form.
Using it this way