Just found this, and it's gorgeous, so I'm putting it here so I don't forget it.
The Sherman Calliope is a special Sherman model that uses a roof mounted rocket artillery array. Its rocket strikes have no resource costs, but has a long cool-down time. It's range is shorter compared to other artillery units.
It's effective against enemy armor and foot soldiers It has a hull mounted 30. cal MG, marginal protection from heavier tanks but the rocket artillery array will make short work of them at shorter ranges.
"Calliope" means musical organ. This name may come from the launcher tubes' resemblance to a pipe organ.
This tanks can only be gained from the American 'Armor Company' command tree choice.
Most Allied commanders use this tank in a 'hit and run' tactic, raining down artillery on enemy concentrations or base areas, before retreating behind other Shermans to avoid counter battery fire or pursuing Panzers. 2 of more of these tanks can dominate a battlefield, making enemy movement near impossible.