The Jackhammer Experimental Unpacking Cannon, is a major experimental introduced with the Infinite War Battlepack DLC. The Jackhammer is a short-range cannon, being able to lock itself into position and unfold a large cannon used for arced bombardment.
While being used as a short-range cannon it is completely immobile, being vulnerable to incoming enemy units. Yet, while being mobile, it appears to have no form of weaponry what so ever, and cannot defend itself. The Jackhammer´s range is way to low to be considered useful, but at least the firepower is decent.
The Jackhammer has a remarkable resemblence to Halo Wars' Cobra & Rhino unit, as they both lock down in a similar manner and turn into powerful artillery-like units. The jackhammer is easily able to take down multiple units killing between 5 to 12 units if in close proximity or if on a bridge (Markon's bridge, for example)
The Jackhammer is probably best explained by comparison to the Fatboy II, a UEF Minor Experimental Land unit.
After all training upgrades, the Jackhammer has 60,000 health, more than some other Major experimentals. By comparison, the Fatboy II has just over 14,000 health after all training upgrades. Jackhammers cost roughly 20% more mass and energy to train, but with over 4 times as much health, they have a much better Mass to Health ratio.
Jackhammers take only 30 seconds longer to train that Fatboy II's if unassisted. Considering the other advantages, unless range is your #1 priority, the Jackhammer is usually the better choice.
Jackhammers move just as fast as tanks, slower than assault bots and considerably faster than the Fatboy II. When a large mass of enemy units is inbound, pack it up immediately and you may be able to get it back to cover before those units can catch it.
The Jackhammer's gun fires a single projectile, 90% as far as the Fatboy II. Despite being a single shot, the Jackhammer's projectile does massive splash damage, enough to destroy level 3 adjacent energy generators in a single shot.The Jackhammer fires once per 5 seconds, Fortified Artillery fires once per 2 seconds. The Jackhammer's DPS is ~65% higher, but will actually work much better against buildings than the Fatboy II, due to the splash radius being so large. It does not track its target, however even Assault Bots cannot move fast enough to not be caught by the splash damage. Jackhammer's muzzle velocity is 30 vs. the Fatboy II's muzzle velocity of 25.
Overall, the Jackhammer is a weaker unit in comparison to the Fatboy II. When trying to take out enemy Fortified Artillery, the range of the Fatboy II should take priority over all the advantages of the Jackhammer. The Jackhammer would have to park and stop within the enemy Fortified Artillery's range to fire at it, whereas the Fatboy II can stay at maximum range and keep moving, destroying it with little or no return fire. The same goes for Illuminate Tactical Missile Launchers - once parked or not moving, a Jackhammer is a sitting duck for TMLs.
Jackhammers do not have to be used offensively to be devastatingly effective. In fact, if parked near a forward base, they will serve quite well as turrets. Their range falls squarely between Heavy Point defense and short range artillery. Jackhammer range: 90, Fortified Artillery range: 115, PD range: 40, and they can be used to "thin out" even the heaviest ground force, lightening the load on your stationary defenses considerably. If placed within range of choke points with proper AA and repair support, 2 Jackhammers can easily destroy anything that attempts to pass through indefinitely. The new UEF Combat Engineer and a few Wasps or Anarchists make excellent partners for Jackhammers in this role.