A submarine’s ability to submerge gives them 4 depth options. Depth options are declared during the Non-Combat Movement Phase. Submarines remain at the declared depth until the players next Non-Combat Movement phase.
This is the default depth of all submarines. Submarines at this depth attack, defend, and move normally. While surfaced submarines block convoy routes. Surfaced submarines are obviously not concealed so may be attacked normally without the need for detection rolls.
While at periscope depth submarines may attack targets with a +1 (D6), +2(D12), or +3(D20) to their attack rolls. This bonus is not cumulative with other bonuses. Submarines at periscope depth defend normally. However, while at periscope depth a submarines movement is reduced to 1. While at periscope depth submarines block convoy routes. Submarines at periscope depth are well concealed, and would require air units (fighter, tactical bomber, or bomber), or destroyers to make a detection roll in order to attack them.
Each unit attempting to search for enemy submarines must first be moved into the sea zone containing the submarine during the combat movement phase. Any other naval units in the sea zone may attack the submarine as well once (and if) the submarine is found. During the combat phase each unit searching for submarines would receive a detection roll. On a roll of 3 (D6), 6 (D12), 10 (D20) or less, all submarines in that sea zone would be located, and are subject to attack. It only takes one successful search roll to find all submarines in a single sea zone. If all the searching units fail to find the submarines, all the submarines in that sea zone would be safe from enemy attacks for that round. Units used to search for submarines are allowed to participate in combat in the same sea zone as well, however would not be allowed to participate in any other combat situations.
If attacking a sea zone with both submarines and other naval units the attacker must roll to search for submarines before combat begins in order to score hits on those submarines. If the attacker fails to find them or elects to not search for the submarines, the submarines could not be taken as casualties even if the defending player would like to do so. However, if the attacking player has brought naval units (other than submarines) into the combat zone the defending player may elect to defend with the submarines. If this occurs the submarines would be subject to attack the following rounds.
Submarines have the unique ability to retreat when defending. To do this the attacking player is allowed attack rolls for the first cycle of combat. Any surviving submarines may forgo their defensive rolls and retreat from combat. Retreating submarines only submerge and avoid detection so they must stay in the same sea zone. Once retreated those submarines may not be attacked again until the next players turn; nor can they reenter an ongoing naval combat they retreated from. This submerged retreat does not change the submarines depth status.
While submerged submarines receive a -1 (D6), -2 (D12), -3 (D20) to their attack and defense rolls. Movement is also reduced to 1 while submerged. While submerged submarines block convoy routes. Submerged submarines are more difficult to detect than subs at periscope depth. Enemy units searching for submerged submarines are successful on a roll of 2 (D6), 4 (D12), 7 (D20).
While in silent running submarines may not attack, defend, move, block convoy routes, or be detected.
Miscellaneous submarine depth status options:
· Depth options are declared during the combat movement phase. (This option may make submarines very powerful, giving the Axis and advantage.)