Monkey Buccaneer and Monkey Sub get +1 pierce per shot.
~ BTD6 description
Naval Upgrades is an upgrade in the Military Monkey Knowledge Tree, first released on initial release. It increases the pierce of all Monkey Subs and Monkey Buccaneers by +1. It does not have a prerequisite Monkey Knowledge requirement.
This is very helpful for Grape Shot, as it now increases the pierce amount to 2 per grape, adding much more reliability to the Buccaneer's grouped popping power.
The +1 pierce to base Monkey Sub makes the Monkey Sub more reliable for the early-game in many scenarios, especially versus multiple spaced bloons.
Airburst Darts also gain +1 pierce per dart, making them more reliable early-game grouped popping power.
Adding Naval Tactics essentially restores original pierce for Monkey Buccaneer's dart and grape attacks, 5 pierce and 2 pierce respectively.