Spy Ships are probe esqe ships used by the Galaga Legions.
The spy ships seem to have been built on the planet Galaga.
March to conquest
Around the time the Galaga Legions were creating an intergalactic empire. The spy-ships were used by the Galaga Legions to monitor the Bosconian bombers as they took out their X-Kobo cruisers. Many of them were destroyed however as they were detected on the bombers' radar when a ship's CPU would say "Spy ship sighted" and a bomber would take it down.
The spy-ships don't seem to be armed but their pilots are willing to collide with another ship if neccesary.