The unwanted convoy is an issue which has many viewpoints across the Diplomacy hobby, and which has caused a number of changes in the rules over the years. It is therefore surprising that the issue was actually resolved accidentally, over 25 years ago — and it seems that nobody noticed, including those responsible for resolving it!
It is worth starting by explaining what is meant by the unwanted convoy. At its core is a pair of orders. The first is an army being ordered to move from one coastal province to an adjacent coastal province — e.g. France orders A(Mar) – Pie. The second is an order by an enemy fleet to convoy that unit — e.g. Italy orders F(GOL) c A(Mar) – Pie.
By itself, the unwanted convoy has no effect on the game. The army still reaches its destination as ordered. The problem is when it is combined with other orders. This can lead to two unwanted situations.
The unwanted dislodged convoy can be worse than that. For instance, if England is moving A(Yor) – Lon, and F(NTH) convoys it and is dislodged, then not only does A(Yor) fail to reach London, but the dislodged fleet is now able to retreat to London.
Let's look at these two situation separately. Firstly the unwanted swap.
The unwanted swap can cause surprising results. However, it is very rare that the results are much worse than could have happened through other orders for the relevant units. For instance, in the above example Italy could just convoy his own army, rather than convoy the French army, for the same result. Or for a result that is almost as bad, he could have just supported his army from Piedmont to Marseilles, and dislodge the French army.
If the Italian had had a fleet in Piedmont rather than an army, then Italy can order F(Pie) – GOL and F(GOL) – Mar with the same effect. Or he still has the option to support himself into Marseilles and dislodge the French unit.
All-in-all, the unwanted swap is completely consistent with the general principle of Diplomacy. Each player orders their units, and depending on the orders, the units move. Some players see the unwanted convoy as a "gotcha" — something that just confuses new players unnecessarily. But I don't see why it is any different from the unwanted support — where a player tries to bounce his own unit, and another player supports one of his moves. And if a player really doesn't want his unit to reach the destination, then the simple solution is, don't order it to move there!
Generally, the unwanted swap will only occur when the victim is already in a difficult situation. They are already outnumbered, and the results are no worse than other possible consequences of their position.
So, on to the unwanted dislodged convoy.
The unwanted dislodged convoy is a strange issue. No rulebook has ever categorically supported its existence!
The unwanted dislodged convoy stems from the 1971/76 rulebook. In that rulebook, rule XII.4 states "Ambiguous Convoy Routes. If the orders written permit more than one route by which the convoyed army could proceed from its source to its destination, the order is not void on account of this ambiguity; but if any of the possible routes are destroyed by dislodgement of a fleet, the army may not move."
In order to create the unwanted dislodged convoy, the above rule has to be taken to apply to armies which have multiple routes to their destination, one of which is a convoy route and one of which is overland. But there is nothing in the above rule to say that it applies in this case. Indeed, the title of the rule is "Ambiguous Convoy Routes", not just "Ambiguous Routes". And the rule specifically applies to "the convoyed army", not just "the army". However, it is argued that, by logical extension, this rule also applies where the army has two routes, one by convoy and one overland.
However, in the 1982 rulebook, this rule was changed. In that rulebook, rule XII.4 states "More than one Convoy Route. If the orders as written permit more than one route by which the convoyed army could processed from its source to its destination, the order is not void on account of this ambiguity; and the army is not prevented from moving due to dislodgement of fleets, unless all the routes are disrupted."
Given that the unwanted dislodged convoy is created by assuming that rule XII.4 applies to multiple routes where one is the overland route, then surely this change to the rule means that the unwanted dislodged convoy is no longer applicable. It is impossible to dislodge a fleet such that the overland route is disrupted, and as such, it is impossible to disrupt all the routes. As such, the dislodged convoy has no effect on the army's ability to reach its destination.
Unfortunately, the writers of the 1982 rulebook clearly did not realise that they had resolved this issue, as they added a whole new rule, rule XII.6, which states "Both a Convoy Route and an Overland Route. If an army could arrive at its destination either overland or by convoy, one route must be considered and the other disregarded, depending upon the intent shown by the totality of the orders written by the player governing the army."
This rule is very poor on two levels. Firstly, as I said, it's completely unnecessary. The changes to rule XII.4 resolve the problem that this is designed to fix. But secondly, how do you determine this based on "the intent shown by the totality of the orders written by the player governing the army"? It might be that France's only unit is the army in Marseilles. So France's only order is A(Mar) – Pie. How is anybody supposed to determine the intent based on that?
And as if that wasn't bad enough, the 1999 rulebook makes an even bigger mess of this part of the rules. In order to attempt to resolve this problem, it adds a whole new order — the "move by convoy" order. The idea is that if an army is moving along the coast, it can be ordered to "move" as normal, or to "move by convoy".
Apart from the fact that, as previously mentioned, this whole problem has already been resolved in the 1982 rulebook, this is changing one of the fundamentals of Diplomacy — the basic four orders — in order to fix a situation that hardly ever comes up in a game. And given that one of the things that makes Diplomacy such a great game is the level of depth it manages to create from such a simple set of available orders, that is a serious case of using a sledgehammer to crack a nut.
So to summarise, the unwanted convoy was a problem in the original rules of Diplomacy. However, it was fixed in the 1982 rulebook, and yet people don't seem to have realised this. And the attempts to fix it since have made the situation worse, not better.
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