Intel Acquired Achievement
Collected 24 Dead Drop flash drives
Dead Drop flash drives are small collectibles that can be found throughout the campaign and COOP missions. They will emit a persistent pining sound when you are near them. If you purchase the first upgrade for the Command & Control sector in the Paladin, it will make Dead Drops permanently visible on your HUD.
Buy this upgrade as soon as possible because these flash drives are extremely small and can be overlooked when playing through each set of missions. Once this upgrade is acquired, the flash drives are almost unmissable on your HUD.