By moving into a newly-created stretch of zero time before moving back into real time, enemy timeships expelled the debris and detritus of centuries which would otherwise be introduced to the local continuum and leave tell-tale trails of the ship’s arrival — the gravity spiders were primed to locate such tiny traces and to destroy any timeships they find in the vicinity. It wasn’t realised until later, by the powers adopting such technologies, that it was precisely this unloading of the past into easily-breached pockets of space-time that the gravity spiders had been designed to provoke. The bubbles of zero time could then be harvested by the Houses in the wake of enemy movements and analysed in order to reveal not just the technical specifications of the timeships, but also their recent history.
Furthermore, the occasional bursting of zero time offered a way of pinpointing timeship activity in itself. It was one of the few weapons-technology coups to have been pulled off by the Houses during the War in its first fifty years. Needless to say, the introduction of zero time to the War made proceedings far more complicated by its very nature; the various War-time factions had different "flavours" of time available, and battlefield scenarios had to be planned to take into account the different kinds of battlefield. Zero time was even used as a medium for accessing the otherwise inaccessible world of Utterlost, although eventually even the zero time routes were cut off. (PROSE: The Book of the War)