Underbase Saga
From Transformers Wiki
The Underbase Saga is a story arc that ran near the midpoint of the original Generation 1 Marvel Comics series. It told of the lost Underbase, a vast collection of knowledge stored as patterns of light, which also doubled as a fantastic source of power. Early in the Cybertronian wars, it was launched into space to keep it out of Megatron's hands, and the cube-shaped entity approaches Earth (sounds kinda familiar, doesn't it?) in the present day. Several Decepticon factions vie to claim it for themselves, with Starscream ultimately succeeding.
The story spanned four issues:
The climactic battle at the end is particularly notorious for killing off swaths of characters en masse, many of whom had already lain deactivated for many issues before. Readers in the UK had it even worse, as this story's catastrophic battle was immediately preceded by the character-decimating "Time Wars" storyline.