In the third arc ("The Ant and the Grasshopper"), the enemy object is described as being "0.5th-generation".
What does that even mean? I thought that the very first object to be built was itself already considered 1st-generation. Is a 0.5th-generation object some sort of subpar imitation or something?
Apparently it's a Generation 0.5 due to the fact it was not properly built, as the level of technology of its country was too low.
The technology level of the Oceanian military nation is not high enough to actually build a proper Object, thus the codename of Generation 0.5.
It contains several cheap measures in order to keep it even stable enough to move.
A single main gun is attached to the left side of the sphere. It's a few dozen meters long and reinforced with numerous steel bridge-like wires. It would likely have been fine without them, but there is a risk of the gun damaging itself with its own weight while it's held horizontal for long periods of time. It's a cheap countermeasure that would never have even been considered for a normal Object.
Therefore, since it is a downgraded version of a normal object and built with improper technology, it is called a Generation 0.5.
The prologue and afterword confirm that the Generation 0.5 was a degraded version of the Information Alliance's Gatling 033. The technology and design were given to the Oceanian military nation by the MIB.
