Arimaa/Multi-Piece Swarming Attacks

Objectives and Risks

Swarming attacks are highly dangerous attempts to smother the opponent and/or control an enemy trap with a large number of pieces. This type of attack is only rarely seen in the opening phase of the game, but many players will use this attack if an opportunity arises to blockade an enemy Elephant or work towards a win by immobilization. If a swarming attack is attempted during the opening phase, the attacking play will often either fail miserably and lose a considerable number of pieces in rapid succession, or will succeed brilliantly when the defender is crushed under the weight of the attack.

Note: For simplicity, many examples below will assume that the Gold player is attacking the c6 trap. Naturally, the same theories can apply equally to attacks on all 4 traps.

Reasons to use a Multi-Piece Swarming Attack:

• to smother the enemy so that an entire wing is effectively immobilized
• to establish a space advantage, possibly controlling the center
• to blockade the enemy Elephant, possibly with the intention of freeing the attacking Elephant from the c6 trap
• to create long-term goal threats from burrowed and advanced Rabbits

Summary of risks (assuming Gold attacks the c6 trap):

• If a swarming attack fails, and attacking Elephant is lured away by a counter-attack, the weaker pieces in the swarm will suffer high casualty rates, especially the Rabbits.
• If a Camel is used to secure b6, it may be taken hostage.
• The swarming player's goal defense and/or home trap defense will be weakened due to the high number of pieces required in a swarm attack.
• The attacking Elephant may become blockaded on d6, possibly with friendly Rabbits locked into the d5 and e5 squares.

Ideal Placement of Pieces

A swarming attack often begins with the Gold Elephant on d6. The Elephant may have to get comfortable on that square, because it will often be pinned there for many moves.

It is absolutely essential for Gold to control the b6 square if a swarming attack has any chance of success. A strong piece can be lodged onto b6, or less commonly, a weak piece can be secured on the square by blockading the entire position, preventing the defender from accessing b6. An exception occurs if the enemy Elephant is located on b6, for example in a hostage situation. Because the attacker cannot take the b6 square, it is often best to attempt a blockade, including an attacker on c6. If the attacker succeeds in controlling b6 or blockading the enemy Elephant, it is sometimes possible to rotate the Gold Elephant off d6 in order to pursue the Silver Horses or Camel.

If the attacker can create goal threats, it is beneficial to have a very strong piece on c7. The Elephant should not be stationed on c7 unless there is a very compelling reason, such as a powerful goal threat.

Defensive Systems and Counter-Attacks

In order to understand the best defensive techniques, it is essential to understand the objectives of the attacking player. If the Gold Elephant is pinned on d6 with a Rabbit framed on c6, and a defending Horse is positioned on b6, then Silver can build a sturdy defense by placing the Silver Elephant on c5.

There are only three obvious strategies for the attacker in that situation:

1. Use the Camel to control b6 or drag the horse to the home trap with the idea of luring the Silver Elephant away from c5.
2. Move the Camel to b6 in the hopes of it being taken hostage, then attacking the enemy Elephant with a swarm of potential blockaders.
3. Repeatedly drag defending Rabbits and other small piece towards the c3 trap to gain material and soften Silver's goal and trap defenses.

These positions can be difficult and it is beneficial to study example games in order to learn the strategies.

While it is tempting to counter-attack against the f3 trap - which may be weakened - and/or advance Rabbits against a Swiss-cheese goal defense, actual practice suggests that the defender's best chances may lie in the proper defense of c6 rather than an immediate counter-attack. If Gold can be stopped cold so that the attackers are completely prevented from having any hopes of controlling the c6 trap, the Gold position will often become hopeless and Silver can slowly and safely proceed to build a powerful advantage. Ideally, after the c6 attack is thwarted and the counter-attack begins, Gold will have no choice but to withdraw the Elephant from d6 and suffer massive losses.