"Turtleshellers despise camping and prefer to see things from the front lines. Their armored shell allows them to maintain resilience as they calculate the arc of their anti-infantry mortar. This makes them particularly effective against Snipers whom they would deem as “cowardly”."
The Turtlesheller is a heavily armored Soldier-type of unit trained out of the Barracks. It is like an armored, upgraded version of the Mortar Team, lobbing different types of artillery shells at the enemy, except that its range is only 2-3, restricting it's effectiveness, until rank 3, when it gains its armor piercing attack, which has a range of 1-2.
The Turtlesheller's high armor actually allows it to be placed on the front line to absorb the brunt of attacks, and allows its shells to reach the rear ranks. From the back row, the Turtlesheller's armor only shields it and other units from Dustwalkers, and its attacks can only reach the front enemy row.