Any tactic based on deception is legitimate in Diplomacy. If the deception is exposed, the situation must be returned to that within the rules, unless the game has gone on to such a point that this return would be impractical. Thus if extra pieces are slipped onto the board ("Flying Dutchmen" -- so named because the tactic was first tried by a player of Germany) they must be taken off once the deception is noticed; but the damage they may have done in the intervening moves may not be undone.
If you note that a player has more pieces than he is entitled to, stop and think -- if his added strength works in your favor, do not expose him. If and when it begins to work against you, expose him after a set of orders has been read (when he is no longer entitled to change his orders, because he has seen the orders of another player); his piece must come off at once, and his orders may have relied heavily on it. Demanding that your ally show you his orders is a common tactic, but he may show you one set of orders, and turn in another.
A standard tactic is peeking as another player writes his moves ("military intelligence'"). Once I was playing Italy and had alliances with Turkey and Austria-Hungary under the terms of which the Adriatic, Ionian, and Aegean seas were to be kept free of fleets. Thus secured I occupied Tunis on the second move, raised a fleet, and attacked the French in Marseilles and Spain. I could make no headway against the French, so we signed a treaty; I pulled my fleets back, and France subsequently sent her armies north. It was now necessary for me to look east for expansion.
Relying on our alliance, Turkey had attacked Russia in the Black Sea area. Germany had come down on A.-H. with armies, occupying Vienna. This crippled A.-H., without really giving Germany much strength, because her southern armies could not co-operate with her fleets. Therefore the area was "Balkanized" and was a good prospect for expansion. I threw my fleets into the neutralized seas. With the Turkish navy tied up in the Black Sea, I was able to capture Greece by attacking from the Aegean with support from the Ionian. Germany, hoping for support in the area, supported my army into Trieste.
My armies were now deployed thus: 2. Trieste, 1. Venice, 3. Rome. Rather than attack a supply center on the following move, I chose the mobilizing moves 2. Albania, 1. Trieste, 3. Venice, which would give me the largest military force - three armies - between the Adriatic and the Black Seas.
When the time came to read these moves, however, I couldn’t find them. A lengthy search failed to produce them. It seems Turkey and A.-H. had quietly taken them. As we were playing in a laboratory engaged in defense work (strictly on our own time - it was about 10:30 p.m.), there were padlocked waste baskets around, intended "for classified waste only". My orders to my armies and fleets were at the bottom of one of these baskets.
As I had not gotten orders through to my units, they stood in place instead of moving. Fortunately, the interception of these orders ("by an Austrian spy") had not been coordinated with an attack on my positions. I was able to carry out my shift to the east side of the Adriatic on the following move. I swept through the disorganized Balkan area and had acquired 13 units, with a demonstrable win of three more by the end of the game.
Reprinted from The Dispatch No.1 (1960)