"Attention all personnel, attention all personnel, main cannon attack countdown thirty seconds. Target coordinates have been sent, all main cannons concentrate fire, charge at 50%," as the master control system announced, the battle hammer defense systems in front of all the warships quickly dispersed, revealing the ferocious main cannons within.
A first-class warship carries two main cannons, and so does a second-class warship. It's not that more main cannons couldn't be fitted, but because the energy consumption of the main cannons is horrifyingly high. The main engine of a spaceship could at most support the full charge of two main cannons—any more would be pointless.