User blog comment:Strife237/Metal Gear Sonic 17/@comment-20015702-20140603142022/@comment-26113388-20140603142749

Actually a stealth suit (despite its name) is a small device that one wears which renders them completely invisible by bending light around them. The fact that Tails had his suits stolen explains how there were four soldiers in the elevator with Sonic even though he couldn't see them.