The Heavy Artillery is a premium artillery unit, capable of high damaging indirect fire. It is a big step up from the Light Artillery, albeit costing 45, but just a predecessor to the even stronger artillery units such as the Earthshaker and eventually the Peacemaker.
The primary attack, Shell Strike, with its high damage potential and superbly high offense allows the Heavy Artillery to strike at the enemy support units or blasting away armor from light vehicles. Because of this, only two Heavy Artillery can get the job done where three weaker artillery units are needed for the same effect.
The Heavy Artillery was on sale for 30% off for a very limited time, and one of very few units to ever be put on sale from its original price.