Shoots larger bombs, they have a larger blast area and more popping power.
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~ BTD6 description
“
Bombs hit a larger area.
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~ BTD5 description
Bigger Bombs is the first upgrade to the Bomb Tower in Bloons Tower Defense 4, the first upgrade of path 2 in Bloons Tower Defense 5, and the first upgrade of Path 1 in BTD6. As it says in the description, this upgrade allows the tower to fire bigger bombs that affect a larger area, popping more bloons (50 in BTD5 and earlier, 28 in BTD6).
Bigger Bombs looks very similar to the regular bomb tower. All that changes is that the bombs turn red, and the appearance of a target on the back of the Bomb Tower. After all, all that really changes is how big the explosion is.
Bigger Bombs doesn't increase the projectile speed or fire rate.
BTD5 and BTD6 are the only games that the icon for Bigger Bombs is not a Pyrocumulus cloud, because it would make sense this way.
In BTD5, bombs fired by a Bigger Bombs Tower are red.
Since the bombs are bigger, they're more likely to hit Bloons than normal bombs. However, since they don't move as fast as a Missile Launcher, they're still less effective than could be conceived.
The BTD5 artwork depicts a multi-sided figure with a red ring around the tip of the tower, but in reality, it simply has a target on it.
The BTD5 artwork shows the Frag Bombs Bomb Tower shooting a red bomb, unlike BMC, it shows the correct tip of the cascable (the backside of a cannon).