The Submarine is a underwater naval vessel commonly used for ambushing and sinking ground unit transport boats and capital ships.
The submarine is significantly effective for annihilating capital ships, such as those with battleships and aircraft carriers, as well as sinking transport ships efficiently, without taking any damage. However, they are extremely vulnerable to escort ships, such as destroyers, and, to a lesser extent, frigates.
Submarines are stealthy in that they cannot be spotted by an enemy from a distant range, as they are hidden underwater when not engaged in combat. However, the nation that owns the convoy as well as their allies, are able to see the submarine's properties, such as the location and division size, until ties are severed. Other factors that one can see a foreign submarine is by engaging in close-combat with it, predicting the submarine's position by moving a unit near to it without participating in war, or implanting sonar stations in the coastlines.
Strengths & Weaknesses
Counters
Weak Against
Usage
Submarines are often used in gameplay. They are hidden to everyone except you and your allies, unless they are close to shore, sonar stations or other ships. Therefore, it is possible utilize the natural cloaking and the element of surprise that comes with it to create a stealthy yet deadly attack.
Their most common use is to attack transport ships which are often sent by players over the sea, unprotected. They are also used in Naval Stacks where their purpose is to counter battleships.
Costs
A Submarine costs $30,000,000 and 5,000 manpower, with an additional upkeep of $340,000 and a consistent consumption of 0.5 units of 
Oil per 5 days.
Unit Modifiers
Work in Progress.
Tactics
Spying
As submarines are invisible yet still let you see the numbers of units near them, they can be very useful for sneakily collecting information from far off nations. Especially useful while planning Naval Invasions so you know how many units are waiting for you.
Coastal Defense
Coastal defense is a common strategy for the use of submarines. You can effectively deny a Naval Invasion if your opponent did not bring destroyers or frigates along with them.
Baiting
Find a spot where naval warfare is common, for example through a strait. Position a single Destroyer, Frigate, or even 1 unit of infantry for minimum casualties there. Then put a few submarines behind it. If your opponent is overzealous they will simply send many battleships to wipe out that single destroyer. You may lose your destroyer in this process, but don't worry. Send your submarines to sink the battleships, and since there are multiple submarines, your opponent wouldn't be able to react fast enough before they lose their battleships. Then, your opponent would've lost many battleships and all you've lost is a single destroyer! Eventually they may wake up to the deadly attacks of submarines and build destroyers... but not until they've lost their capital ships already.
Try to ONLY use this strategy against inexperienced players and countries that mainly use battleships for naval dominance. Also this will be extremely devastating to less wealthy countries since battleships are very expensive to build, making them hard to replace for the enemy.
Obstacle
With enough submarines and strategic ambition, you can force enemy ships and transports to go a desired route through sea by forming walls of submarines to force them in that direction. Think of it like a maze. If enemy transports and ships go in different directions, they will hit your submarine walls and sleep with the fishes.
Trivia
- The submarine is the only naval unit that cannot subdue aircraft.
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| Units | ||
|---|---|---|
| Army | Primary | Infantry • Tanks • Home Guard |
| Support | Artillery • Anti Aircraft | |
| Navy | Escort | Destroyer • Frigate • Transport Boat |
| Capital | Battleship • Aircraft Carrier | |
| Underwater | Submarine | |
| Air Force | Fighter • Attacker • Bomber • Transport Aircraft | |
| Nuclear | Nuke | |
| April Fools | Nuke (April Fools) • Space Units | |
| Mechanics | ||
|---|---|---|
| Strategic | Doctrines • Operations • Attrition • Entrenchment • Flanking • Auto Capture | |
| Leadership | Military Leaders • Traits • Political Leaders | |
| Logistics | Manpower • Experience • Military Power • Conscription Laws • Readiness • Military Spending • Recruitment Centers • Reinforcements | |
| Other | Technology • War Exhaustion • War • War Justification • Skins | |