Erich's warships protected the frontier, forming a thin line between the settled portions of Germanic Space, and the Naraku invasion. Unlike his peers, the Germanic Navy had done an excellent job of containing the threat. No doubt because of their ability to rapidly identify the Queen Ships and annihilate them.
To put it simply, the Naraku had no real answer to the cannons which the Germanic Dreadnoughts were built around. The moment a Queen died, her entire fleet would turn feral, attacking everything in the vicinity, and it just so happened that the Naraku Fleets were far closer to their allies than their enemies.
It was an excellent strategy. One which the Naraku had not anticipated. But one that Tia and Erich had come up with together. An incredible amount of time had gone into researching what could be used to identify a queenship over its normal counterparts.
