"Order the Gardes to fall back, and fire the Heavy Mass Cannons."
"It'll only provide temporary relief."
The Heavy Mass Cannon is the Sidonia's more commonly used defense weapon.
When Gauna 487 makes it's attack on Nagate Tanikaze's mining squad, Kobayashi orders the Gardes to fall back and to fire one of the Heavy Mass Cannons. She acknowledged that it was only a delay tactic, but it would at least push back the Gauna until Sidonia could make a plan to deal with it. The round made a direct hit, vaporizing the ena but the core was unhurt.
When Gauna 487 returned and tore through Akai squad, the Sidonia fired another round at point blank, but the Gauna used destroyed Akai squad's Gardes to swing itself around the bullet, leaving it unhurt and still on collision course.
In comparison to the ship the cannon looks small, but fires a massive concave-ended metal cylinder big enough to atomize a huge asteroid. Ammunition propulsion is not specified, most likely by use of intensified magnetic fields but it also could be a compressed nuclear blast. Whatever the method, the shell is propelled rather slowly, using sheer weight and size to do damage.
Sadly, in spite of this weapon's immense power, it cannot even nick a Gauna core.
- Following Eiko Yamano's death, Nagate Tanikaze has a grisly reccuring nightmare involving stomping her beneath his boot, and then she is squished beneath a HMC round.
- When fired, the muzzle flash from the cannon resembles a blue nuclear fireball.