A defining characteristic of naval campaigns is uncertainty about what lies over the horizon. These rules introduce this element of uncertainty into Modern Naval Battles and I recommended using these for the scenarios I published previously.
Representing hidden ships and submarines this we introduce radar and sonar blips into the game. Blips represent the uncertainty of identifying the identity, size and composition of enemy fleets at a distance.
For one reinforcement point each (representing the cost of E.C.M.), a player can buy two radar or sonar blips and place them as hidden cards in the second or third rows at the start of the game. If bought as a reinforcement, the blip cannot be placed in the first row.
Each radar blip is either a ship (not submarine) represented by placing the card face-down or a dummy card using a ship card from another navy.
If a concealed ship takes an action, or moves to the first row or enemy successfully attacks (see below) the radar blip, the card is turned over, if the card is a dummy it is immediately removed.
Submarines have sonar blips instead of radar blips, these operate in the same way, but cannot be spotted by adjacent ships or submarines in their first row. Submarines that "go active" immediately become visible to the enemy.
The enemy can launch missile, torpedo, bomber strikes or airstrikes attacks against a radar blip or ASW attacks on a sonar blip if in range, but due to the uncertainty about the enemy's exact position, they may miss. To see if the attack fails to locate the target, first see if the attack is successful (if applicable). If the attack was successful, the radar blip gets an Evasive capability of '6' if two rows away from the firing ship, or '3' if a sonar blip, or a radar blip further away from the firer.
If the radar or sonar blip successfully evades the attack, it remains hidden. If the evade fails, then the blip is revealed to be either a dummy and is removed, or a ship or submarine which takes then takes any damage from the attack.
A player can, of course also play defensive cards (i.e. Intel, Near Miss or Screening Ship) on any radar or sonar blip under attack. Also if a ship has intrinsic Evasive capability this can be applied to any successful attacks.
Additionally, an intel card may be used to spot any enemy radar blip.