Activate submerge using target option to permanently reveal camo bloons in its radius.
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~ Description from BTD 5 iOS
Submerge and Support is the 3rd upgrade on Path 1 for the Monkey Sub in BTD5. It costs $425 on Easy, $500 on Medium, $540 on Hard and $600 on Impoppable. It adds a new Submerge targeting option. When selected, it stops firing darts, however, it starts removing camo from Bloons in its range, including DDTs (both BMCM).
In BTD5 generation games, the target settings must be changed manually to use the "Submerge" option, though in BTD6 it automatically changes to "Submerge" targeting upon upgrading.