Triple Guns is the third upgrade of Path 3 for the Monkey Sub in BTD6. It adds a third gun to the Monkey Sub that increases the attack speed by a further 50%, in total shooting 3x as fast as a normal Monkey Sub. The third gun is functions exactly the same as the other two.
It costs $935 on Easy, $1,100 on Medium, $1,190 on Hard and $1,320 on Impoppable.
Before Version 7.0, it was more wise to purchase more Triple Guns than purchasing more Armour Piercing Darts when it comes to beating Super Ceramics. With the increased damage buff to Armour Piercing Darts, it is more efficient to upgrade some of the Triple Gun Monkey Subs to Armour Piercing Darts. However, more Triple Gun Monkey Subs are much more useful if pierce is more of a necessity than damage.
Two Triple Guns is more cost-efficient than purchasing three Airburst Darts when it comes to price.
On almost all occasions, it is better off purchasing Advanced Intel for Triple Guns, which maximizes the range that it can attack around. This usually is far superior to both slightly increased pierce from Barbed Darts and simple lead-popping power from Heat-Tipped Darts combined.
One 2-0-3 Sub costs $3785 on Hard Mode, which is particularly useful to know in CHIMPS Mode ($350 + $140 + $540 + $485 + $1080 + $1190).
Triple Guns shoots darts 3x as fast as a normal Sub. Twin Guns shoots darts 2x as fast as a normal Sub. Thus the total attack speed bonus from upgrading Airburst Darts (which as Twin Guns) to Triple Guns is exactly 50% extra.