Age of Empires Series Wiki

Monitor attack and hitpoints increased.
—In-game description
Ironclad attack and hitpoints increased.
—United States and Mexican in-game description

Ship's Howitzers is a technology in Age of Empires III that can be researched by European and Asian civilizations at the Dock once the Industrial Age is reached. Once researched, it upgrades Monitors to Heavy Monitors, which have +25% hit points and attack. In the Definitive Edition, it is also available to the United States and Mexicans, but for these two civilizations, it upgrades Ironclads to Heavy Ironclads, which have +25% hit points and attack.

Dock technologies in Age of Empires III
SharedGill Nets · Long Lines · Armor Plating · Carronade · Percussion Lock · Ship's Howitzers
Native AmericansImproved Cordage*** · River Raids*** · Flag IroquoisDE Rawhide Covers · Flag SiouxDE Flaming Arrows · Flag AztecDE Cipactli Worship · Flag IncanDE Totora Reeds*
Africans**River Skirmishes · Heavy Riverboats
* introduced in the Definitive Edition   ** in The African Royals   *** in Knights of the Mediterranean