Convoy Raiding vs Unrestricted Naval Warfare
Posted: Sun Jul 05, 2026 4:03 pm
In the preceding thread Scout1 asks about the comparative impact on the U.K. of German raiding against U.K. convoy routes versus German unrestricted naval warfare. The answer is not simple and the while the overall effects of both are mentioned in the Manual and the Strategy Guide, the details are not spelled out. So, I thought it would be useful to unpack the effects of each.
Convoy raiding can be carried out by any enemy naval unit (but not by naval mines). It requires placing the raider on or next to a convoy line hex. If the raider is a surface ship, it must be put into "raider" mode (which can be done at the end of a move). If the raider is a sub, it must be in "hunt" mode (which can only be changed before the sub moves).
The effects of convoy raiding are calculated at the end of the enemy's next turn. Raiding costs the raiding unit 1 supply point. Naval units can not raid at 0 supply. Surface ships gain 0.1 experience points per turn; raiding subs gain 0.2 experience points per turn. If the enemy can move a naval unit adjacent to a raiding unit, the effects of the raid will be cancelled. The position of a convoy raider will be marked for the enemy by a ? symbol on the map with a one turn delay.
Raids reduce the MPPs earned from an active convoy route. The losses to the receiving powers can be seen on the screen listing MPPs earned at the end of their turn; the losses inflicted by the raiding power per naval unit can be seen from the combat results listed at the beginning of their next turn. The formula for calculating MPP losses through raiding is complex and depends on: the kind of unit doing the raiding, its strength, the difference between Advanced Subs tech and ASW tech for raiding by subs, and the value of the convoy depending on the season. See Section 5.6.7.5 in the Manual for the exact formula. In general, subs inflict the greatest MPP losses as they have a multiplier of 12; dreadnoughts, pre-dreanoughts and aircraft carriers have 10: battle cruisers, heavy cruisers and light cruisers have 8; destroyers, seaplane tenders and torpedo boats have 5.
Raids also have a small effect on the enemy's National Morale. Subs, dreadnoughts and pre-dreadnoughts inflict 25 NM points per raid; aircraft carriers 20 NM points; battle-cruisers, heavy cruisers and light cruisers 15 NM points; destroyers, seaplane tenders and torpedo boats 10 NM points.
If German naval units are in the North Atlantic, they can trigger a small swing in U.S. mobilization. If that happens, there is a pop-up saying "U.S Protests The Sinking Of One Of Its Merchantmen". If one German naval unit is within 50 hexes of hex 80,87, there is a 4% chance per turn that the U.S. will swing 1-2% towards the Entente. If two or more German naval units are in the same range, there is a 6% chance that the U.S, will swing 2-4% towards the Entente. Note that merely the presence of German naval units within 50 hexes of hex 80,87 can trigger this swing, regardless of whether they are raiding or not.
Unrestricted naval warfare occurs when a German naval unit is on or adjacent to one of the red NM objective hexes on the map west of Great Britain. These hexes are grouped into four zones: the North Channel; the Irish Sea; the Bristol Channel; and the St. George's Channel.
The first time that a German naval unit moves on or adjacent to one of these hexes, Germany will receive a DE asking if it wishes to launch unrestricted naval warfare. If Germany says YES, unrestricted naval warfare will happen every turn for the rest of the game provided that Germany has a naval unit on or adjacent to one of these hexes. If Germany says NO, unrestricted naval warfare will not begin. However, Germany will receive the same DE again when it moves a naval unit on or adjacent to one of these hexes after the U.S.A. enters the war. At that point, there are no downsides for Germany to saying YES to launching unrestricted naval warfare.
While subs are the most common naval units used for this purpose, any German naval unit including naval mines can be used to launch unrestricted naval warfare. (In theory, naval units of other CP powers could carry out unresticted naval warfare, but in practice that would only happen under very unusual circumstances).
Note that unlike convoy raiding, there is no supply cost for naval units practicing unrestricted naval warfare. However the German naval units practicing unrestricted naval warfare must have a supply level of 5 or higher.
The only intelligence that the U.K. will automatically receive about unrestricted naval warfare is a pop-up at the beginning of a friendly turn that Germany is carrying it out in a given zone.
For each NM hex that has a German naval unit on or adjacent to it, the U.K will lose 75 NM points per player turn. For each NM zone that has a German naval unit carrying out unrestricted naval warfare, Germany will earn 75 NM points per player turn.
In addition, each player turn that Germany has one or more units practicing unrestricted naval warfare in the following zones, the supply level of the three convoy-receiving ports on the west coast of Great Britain will be reduced every player turn, according to the following schedule:
German naval units in the North Channel: Glasgow loses 1-2 points; Liverpool 1-2 points
German naval units in the Irish Sea: Glasgow loses 0-1 points; Liverpool 1-2 points; Bristol 1-2 points
German naval units in the Bristol Channel: Liverpool 0-2 points; Bristol 1-2 points
German naval units in the St.George's Channel: Liverpool 1-2 points; Bristol 0-2 points
Note that to have this effect, the German naval units must be on one of the NM hexes in that zone; there is no effect on U.K. port supply if the naval units are adjacent to one of these hexes. It is sufficient to have just one unit carrying our unrestricted naval warfare in a given zone to have this effect. If Germany can have units in more than one zone, it will increase the speed by which UK ports lose supply. Once a given port falls below level 5 supply, it will cease to receive convoys until it can regain level 5 supply. Ports will regain 1 supply level per friendly turn once there are no longer German units carrying out unrestricted naval warfare in a relevant zone.
For each player turn that Germany is carrying our unrestricted naval warfare in any zone, there is 75% chance that the U.S.A. will swing 1-4% towards the Entente. These odds do not change if more than one German unit is carrying out unrestricted naval warfare. Note also that from May 10 1915 onwards, if Germany is practicing unrestricted naval warfare, there is a 50% chance each turn that Germany will sink the Lusitania, which will swing the U.S.A. another 5-8% towards the Entente.
In sum, convoy raiding is useful for reducing the enemy's convoy income immediately and for gaining experience over time. For Germany, there is a small risk each turn of triggering a reaction from the U.S.A if Germany is raiding the convoy lines to the U.K. in the North Atlantic. However, the loss of supply each turn means that raiding can only be carried out for a limited number of turns before the raiding units have to return to port to resupply. Convoy raiding can be carried out far from any enemy ports, though that means the German raiding units will have further to travel to get back into supply.
Unrestricted naval warfare must be carried out close to the western approaches to the U.K., and thus within scouting and striking range of Entente naval units and aircraft. It will have a much bigger negative impact on U.K. MPP income if it is sustained long enough to shut down one or more of the U.K.'s convoy-receiving ports. It also imposes a greater NM cost for the UK and a tangible NM gain for Germany. As there is no loss of supply involved, a campaign of unrestricted naval warfare can be sustained for as long Germany can keep one or more naval units on at least one NM hexes. These effects however come at the cost of a significantly higher risk each turn of triggering U.S. mobilization towards the Entente.
Convoy raiding can be carried out by any enemy naval unit (but not by naval mines). It requires placing the raider on or next to a convoy line hex. If the raider is a surface ship, it must be put into "raider" mode (which can be done at the end of a move). If the raider is a sub, it must be in "hunt" mode (which can only be changed before the sub moves).
The effects of convoy raiding are calculated at the end of the enemy's next turn. Raiding costs the raiding unit 1 supply point. Naval units can not raid at 0 supply. Surface ships gain 0.1 experience points per turn; raiding subs gain 0.2 experience points per turn. If the enemy can move a naval unit adjacent to a raiding unit, the effects of the raid will be cancelled. The position of a convoy raider will be marked for the enemy by a ? symbol on the map with a one turn delay.
Raids reduce the MPPs earned from an active convoy route. The losses to the receiving powers can be seen on the screen listing MPPs earned at the end of their turn; the losses inflicted by the raiding power per naval unit can be seen from the combat results listed at the beginning of their next turn. The formula for calculating MPP losses through raiding is complex and depends on: the kind of unit doing the raiding, its strength, the difference between Advanced Subs tech and ASW tech for raiding by subs, and the value of the convoy depending on the season. See Section 5.6.7.5 in the Manual for the exact formula. In general, subs inflict the greatest MPP losses as they have a multiplier of 12; dreadnoughts, pre-dreanoughts and aircraft carriers have 10: battle cruisers, heavy cruisers and light cruisers have 8; destroyers, seaplane tenders and torpedo boats have 5.
Raids also have a small effect on the enemy's National Morale. Subs, dreadnoughts and pre-dreadnoughts inflict 25 NM points per raid; aircraft carriers 20 NM points; battle-cruisers, heavy cruisers and light cruisers 15 NM points; destroyers, seaplane tenders and torpedo boats 10 NM points.
If German naval units are in the North Atlantic, they can trigger a small swing in U.S. mobilization. If that happens, there is a pop-up saying "U.S Protests The Sinking Of One Of Its Merchantmen". If one German naval unit is within 50 hexes of hex 80,87, there is a 4% chance per turn that the U.S. will swing 1-2% towards the Entente. If two or more German naval units are in the same range, there is a 6% chance that the U.S, will swing 2-4% towards the Entente. Note that merely the presence of German naval units within 50 hexes of hex 80,87 can trigger this swing, regardless of whether they are raiding or not.
Unrestricted naval warfare occurs when a German naval unit is on or adjacent to one of the red NM objective hexes on the map west of Great Britain. These hexes are grouped into four zones: the North Channel; the Irish Sea; the Bristol Channel; and the St. George's Channel.
The first time that a German naval unit moves on or adjacent to one of these hexes, Germany will receive a DE asking if it wishes to launch unrestricted naval warfare. If Germany says YES, unrestricted naval warfare will happen every turn for the rest of the game provided that Germany has a naval unit on or adjacent to one of these hexes. If Germany says NO, unrestricted naval warfare will not begin. However, Germany will receive the same DE again when it moves a naval unit on or adjacent to one of these hexes after the U.S.A. enters the war. At that point, there are no downsides for Germany to saying YES to launching unrestricted naval warfare.
While subs are the most common naval units used for this purpose, any German naval unit including naval mines can be used to launch unrestricted naval warfare. (In theory, naval units of other CP powers could carry out unresticted naval warfare, but in practice that would only happen under very unusual circumstances).
Note that unlike convoy raiding, there is no supply cost for naval units practicing unrestricted naval warfare. However the German naval units practicing unrestricted naval warfare must have a supply level of 5 or higher.
The only intelligence that the U.K. will automatically receive about unrestricted naval warfare is a pop-up at the beginning of a friendly turn that Germany is carrying it out in a given zone.
For each NM hex that has a German naval unit on or adjacent to it, the U.K will lose 75 NM points per player turn. For each NM zone that has a German naval unit carrying out unrestricted naval warfare, Germany will earn 75 NM points per player turn.
In addition, each player turn that Germany has one or more units practicing unrestricted naval warfare in the following zones, the supply level of the three convoy-receiving ports on the west coast of Great Britain will be reduced every player turn, according to the following schedule:
German naval units in the North Channel: Glasgow loses 1-2 points; Liverpool 1-2 points
German naval units in the Irish Sea: Glasgow loses 0-1 points; Liverpool 1-2 points; Bristol 1-2 points
German naval units in the Bristol Channel: Liverpool 0-2 points; Bristol 1-2 points
German naval units in the St.George's Channel: Liverpool 1-2 points; Bristol 0-2 points
Note that to have this effect, the German naval units must be on one of the NM hexes in that zone; there is no effect on U.K. port supply if the naval units are adjacent to one of these hexes. It is sufficient to have just one unit carrying our unrestricted naval warfare in a given zone to have this effect. If Germany can have units in more than one zone, it will increase the speed by which UK ports lose supply. Once a given port falls below level 5 supply, it will cease to receive convoys until it can regain level 5 supply. Ports will regain 1 supply level per friendly turn once there are no longer German units carrying out unrestricted naval warfare in a relevant zone.
For each player turn that Germany is carrying our unrestricted naval warfare in any zone, there is 75% chance that the U.S.A. will swing 1-4% towards the Entente. These odds do not change if more than one German unit is carrying out unrestricted naval warfare. Note also that from May 10 1915 onwards, if Germany is practicing unrestricted naval warfare, there is a 50% chance each turn that Germany will sink the Lusitania, which will swing the U.S.A. another 5-8% towards the Entente.
In sum, convoy raiding is useful for reducing the enemy's convoy income immediately and for gaining experience over time. For Germany, there is a small risk each turn of triggering a reaction from the U.S.A if Germany is raiding the convoy lines to the U.K. in the North Atlantic. However, the loss of supply each turn means that raiding can only be carried out for a limited number of turns before the raiding units have to return to port to resupply. Convoy raiding can be carried out far from any enemy ports, though that means the German raiding units will have further to travel to get back into supply.
Unrestricted naval warfare must be carried out close to the western approaches to the U.K., and thus within scouting and striking range of Entente naval units and aircraft. It will have a much bigger negative impact on U.K. MPP income if it is sustained long enough to shut down one or more of the U.K.'s convoy-receiving ports. It also imposes a greater NM cost for the UK and a tangible NM gain for Germany. As there is no loss of supply involved, a campaign of unrestricted naval warfare can be sustained for as long Germany can keep one or more naval units on at least one NM hexes. These effects however come at the cost of a significantly higher risk each turn of triggering U.S. mobilization towards the Entente.