The Culverin is not very effective against anything other than buildings, artillery and ships, but makes up for this fact by being extraordinarily good at its two primary functions, namely taking down artillery and ships, and can protect a large area. In comparison to other units, it deals more damage versus ships than the HaudenosauneeLight Cannon (400 vs 210 unupgraded). While it doesn't match the extended range of the Mortar or Morutaru, it is far more accurate against a moving ship.
Unless an opponent is building cannons or a strong navy, Culverins have little use in most games. Some may want to keep a few around just in case of a ship or artillery attack, while others would consider it a waste of resources to build a unit which doesn't counter anything currently in play.
Due to their sizeable range, Culverins can adequately defend a shoreline from most ships as they have more range than all ships except Monitors and Ironclad. Not even the ships using "Offshore Support" or "European Cannons" will have a greater range than a Culverin, they come up one point short of matching its range. When combined with the even higher anti-ship range of Outposts and Town Centers built near the water and walls along the shore (preventing troops from being unloaded), the player will be safe inside their turtle shell until Monitors are able to be produced by the enemy.
Asian civilizations can get Culverins by allying with Portuguese and Russians at the Consulate which provides armies and technologies that includes Culverins listed below. Unlike their regular counterpart, these Culverins are automatically upgraded in the Industrial Age and the Imperial Age (see here for the exact values).
Although it is not listed in the patch notes, since update 38254, Culverins now have an additional ×4.0 multiplier against Gatling Camels.
With update 13.4412, Culverins have a ×2.0 multiplier against buildings and Gatling Camels. This makes their total damage multiplier against Gatling Camels ×4.0.
Knights of the Mediterranean
With update 13.9057, Culverins have a ×1.9 multiplier against buildings.
The Culverin gets its name from the Latin word for serpent – colubra – used to describe the cannon's distinctive curving handles. It was a long, heavy cannon and could fire at great range. A skilled team of gunners could use the Culverin's extreme range and precision to target specific enemy buildings or defenses.
A Culverin in Bombard mode
A Culverin in Limber mode
An Imperial Culverin Royale in Limber mode
A Culverin Royale in Bombard mode
A real-life culverin
A Culverin side view
Culverin in the original version and Definitive Edition