Rapid Reload (BTD4-BTD5)

Rapid Reload is an upgrade for the Mortar Tower in BTD4 and BTD5 that makes it fire faster. It costs $170 on Easy, $200 on Medium, and $215 on Hard in BTD4. In BTD5 it is the first tier upgrade on Path 2, costing $210 on Easy, $250 on Medium, and $270 on Hard and $300 on Impoppable.

Trivia

 * Throughout the series, the Rapid Reload upgrade has always become more expensive. Similar pattern occurs for Crow's Nest; coincidentally they both debuted in BTD4.