Arimaa/Attacking/Techniques

A trap attack plan must consider the whole board. If an attacking piece is taken hostage by the enemy elephant, and the attacking elephant defends the hostage, that is an elephant deadlock. An elephant-less attack may then occur on the other wing. If the hostage is a camel, and the hostage-holder's own camel is already on the other wing, the hostage-holder's position may be strong. If the hostage is a horse, however, and both camels are free, the hostage-holder's position is likely weak, and the original attacker likely has the advantage. This informs opening strategy. A horse often advances early, and is willing to be taken hostage. Other pieces, including the camel, may advance behind the horse; EMH (elephant-camel-horse) attacks are common in the opening. Once strong pieces are captured or marginalized, further attacks may require less strength.

Course of an EMH attack

When camels are on opposite wings, each side might advance on its camel wing, with a potential EMH attack in mind. If full-blown EMH attacks occur on both sides, the game could be over quickly, with the loser having miscalculated the position. Typically, one elephant or camel will end up defending its home trap and perhaps punishing an enemy attack.

Advance pieces

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Most often, an elephant and horse are the first pieces to advance into enemy territory. An advanced horse might pull an enemy piece homeward, unfreeze a friendly piece from above, or participate in a trap attack. If a silver horse occupies b6, a gold horse may initially advance to a6, hoping to later get onto b6. Likewise, a silver horse may go to h3 in hopes of later getting onto g3. Anticipating such a countermove, Gold blockaded h3 with rabbits; the silver horse can still reach h3, but that will now take at least six steps. Gold is willing to let his eastern rabbits be pulled while he develops in the west.

If her camel switches wings, Silver might get a strong horse-by-camel hostage. To prevent this, the gold elephant might quickly advance to e6 or d6.

A gold rabbit might also soon advance on the a-file, though unlike a horse a rabbit can never retreat homeward. If the gold camel advances, Gold will likely move a different piece onto b3, both to defend c3 and to support the attack on c6.

Occupy key square

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In this diagram, Gold has just played the pull-and-replace Mb4ns hb6s Ha6e, getting his horse onto b6. Note that the a5 rabbit allowed the camel to return from b5 even with the silver elephant on c5. The b3 rabbit and c3 dog likewise keep the camel mobile; a successful trap attack is usually supported by weak pieces.

The gold camel now threatens to pull the silver horse south and take it hostage, which would give Gold strong threats in both western traps. Silver to move can prevent this by retreating the silver horse to a6, from where it might later get back onto b6 via a pull-and-replace. An immediate pull-and-replace is not advisable for Silver, as the gold camel could then take b6, pushing the silver horse onto a6 so that Silver could not easily take the camel hostage.

If Silver still held b6 as well as c7, the silver elephant might occupy b5 to block the gold camel. Gold might advance on the c-file, with the aim of getting a gold piece through c6 or dragging a silver piece to c3. If the silver elephant continued to block the gold camel on the b-file, the gold camel might eventually go east to defend f3 and/or create a second threat.

If an attacking gold camel finishes a turn on b5 while the silver elephant is on c5, Gold should use congestion to ensure that Silver cannot flip the camel to d5.

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Sometimes it is the camel which occupies a key square. Here, the eastern gold horse helped its camel reach g6. Silver could take the camel hostage, but such a hostage might be weak, as a silver horse is blocked in and Silver is not yet aligned for a western MH attack.

Rotate out elephant

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If a trap attacker can replace his elephant with a weaker piece, the elephant might soon create a second threat. From this position, Silver played 11s De3e ed3e dd4s cf6e, contesting c3 with a camel and dog while also preventing a one-turn capture in f6, which the silver elephant can now defend. The gold elephant must stay by c3 to prevent material loss, so this rotation gives Silver a strong elephant mobility advantage. In other cases, the departure of the attacking elephant might also free the defending elephant, but the lasting shared control should still give the attacker an advantage.

Which piece should replace the attacking elephant depends on what defenders are nearby. In this case, no gold horse was near d3, so a silver dog could do the job. The gold dog on d2 might have allowed Gold to reclaim d3 with a pull-and-replace (12g Ec4ew dd3n Dd2n), but here Silver could undo that with 12s ee3n Dd3e dd4s dd5s, after which the silver dog on d4 would block the pull-and-replace.

Alternative: switch wings with the camel

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In this game, Gold attacked the f6 trap and held two key squares, but could not easily take f7 or replace his elephant on e6. Gold thus kept his elephant in place and moved his camel west, to counter the silver camel and perhaps create a second threat.

Some noteworthy features of the position:

• The g5 rabbit stops Silver from regaining g6 with a pull-and-replace. This defensive pull-and-replace is a common idea, as is blocking it via g5.
• If f6 were empty, the attacking gold horse could reach f7 by first pulling the rabbit and then pushing away the cat. To protect the square behind the trap, a defender might need to occupy the trap square itself.
• Silver should also continue to occupy e7 and especially d6. If Gold could flip the silver horse to d6, the silver army would be unbalanced, and a gold dog could become a strong eastern attacker.
• If Gold has time to advance the h2 rabbit to h6, Silver will be cramped in the east.

Defences

When one's home trap is threatened with a multi-piece attack, simply adding a defender is likely not enough. Even if an elephant defends its trap, the attacker might take strong shared control and then create a second threat. An effective defense must limit the attacker's options, and perhaps punish the attack.

Counterattack

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Silver defended f6 and attacked f3.

Often, the best response to a trap attack is a trap attack. A counterattack usually occurs on the other wing, but can occur on the same wing if that is where the opponent is weakest. In this game, Gold attacked f6 and then Silver attacked f3; Silver's attack is far stronger, and the silver elephant could likely stop any further attack by Gold. With his home forces unbalanced, Gold could do little about Silver's eastern advances. Had the gold camel been in the east, it would have been much harder for Silver to counterattack there, and Gold's attack would have been stronger.

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Gold answers an EMH attack with an MH attack, while the gold elephant defends. (Game)

If an EMH attack occurs on each wing, the one who attacked first will likely be ahead. An MH attack may be a better response to an EMH attack; with the elephants deadlocked on the EMH attack wing, the MH attacker's camel would be the strongest piece on the other wing.

Bring the camel

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The silver camel aims to get the gold horse off of b6. (game)

The camel is the ideal piece to fight an advanced enemy horse, and the strength of an attack often depends on the attacker's ability to keep the defender's camel away. To protect its horse, an advanced elephant might step directly into the camel's path or pull a back-rank rabbit to block the camel.

Even if the camel can reach an attacking horse, the attacking elephant might displace the camel. If the camel is pushed or pulled toward the attacker's home trap and can't easily step back, the attacker may have strong threats in two traps. Furthermore, a camel could get overloaded by measured horse advances on both wings. A horse-by-camel hostage will tend to be strong when the camel is supported by a friendly horse, as this will usually allow the friendly elephant to go elsewhere and create a second threat. Otherwise, such a hostage may be quite weak.

In this game, the gold camel punished Silver advances on both wings.

Blockade squares

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Gold and Silver have each used phalanxes to block access to key squares. (Game)

To deny the attacker access to key squares, the defender might blockade them; the defender might also blockade the trap square itself, so that an attacker can't move through it. An attacker may then have to resort to pulling pieces homeward. A defending piece on a trap square might later step off to defend against capture; a trap defender must watch for one-turn capture threats, especially those which could be executed via a pull, which may be less obvious.

Rabbit blockade

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Gold's own rabbits block his planned eastern attack.

In this game, Gold advanced a rabbit to h5 so that his camel could move through g5, perhaps for a pull-and-replace. Silver foiled this plan by pulling another gold rabbit to g5. Since rabbits can't retreat, the g5 and h5 rabbits now block other gold pieces. Silver should keep these gold rabbits in place, so as not to reopen an attack path for the gold camel or allow the h6 horse to retreat.

A flank rabbit advance may aid an attack, but only if a clear path is left for an attacker.

Horse-by-elephant hostage

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Gold's horse hostage slows Silver's attack in the east, and Gold has a threat in the west.

An attacker should not take for granted that a horse-by-elephant hostage would be weak; this depends on the whole board and on subsequent gameplay. By the time the silver horse was hostaged in this opening, the gold camel had advanced and couldn't be captured in exchange for the silver horse alone; having pieces on c6 and f5 complicated things for Silver.

In other cases, a horse-by-elephant hostage might be converted to a frame or horse-by-camel hostage. An attacker should try not to allow time for such counterplay. A horse advancing on the edge might sometimes stop at the fifth rank or go to the seventh, to avoid being hostaged right away.

Maneuvers

Below are some ways a trap attacker might take or hold a decentralized key square. There is no simple recipe for attacking; any maneuver might be thwarted, and the whole board must be considered. Advancing too many pieces could leave one's home defense thin, perhaps allowing the opponent to get a strong counterattack. The following are simply some common tactics that both sides should be aware of.

The positions are all from linked games, but are moved to the northwest quadrant, with colors swapped when necessary.

a b c d 8 7 6 5 game	The gold horse dives through the trap: Hb5en cc7n Hc6n. This may be dangerous for Gold if the silver camel is at home; even if the camel can't immediately take the gold horse hostage, the silver elephant may block the horse from retreating while the silver camel comes west. Unless the attacker is well-developed on the wing, a horse-by-camel hostage behind the trap will tend to be strong, as the camel will usually have support at home. To prevent such a dive by Gold, Silver could use a phalanx to blockade c7, or blockade the trap itself. Gold might then pull or flip pieces toward c3.
a b c d e 8 7 6 5 4 game	Gold to move defeats the c7 phalanx with Ed6e cd7s cc7e Hc6n. The gold piece on c5 is essential; without it, the horse would be lost when the elephant stepped away. Silver to move could frame the gold horse, although Gold might soon break that frame via a pull-and-replace.
a b c d 8 7 6 5 game	Silver has blockaded b7 against the advanced gold horse, but Gold defeats the blockade with Ed7s dc7e rb7e Ha7e, setting the stage for the horse to take c7.
a b c d 8 7 6 5 4 game	Gold to move does a pull-and-replace (Mb4ns hb6s Ha6e), creating potential threats in both c6 and c3, as the silver horse could be pulled further south. Since the silver horse remains mobile on b5, Silver can then do a pull-and-replace to frame the gold horse; the frame would not hold for long, but might buy Silver time. Silver to move might place her elephant on b5 to block the gold camel, and perhaps do an MH counterattack in the east.
a b c d 8 7 6 5 4 game	Gold to move could retreat his camel or move it into the trap. Either way, the a6 horse could move to b6. Silver to move could blockade the gold camel and horse with rc8w rd7s Rc5w ec4n or rc8w rd7s ec4wn.
a b c d 8 7 6 5 4 game	Gold just played Rb2nn db6e Mb5n. The a7 horse prevents a camel hostage, unless the camel is blockaded. In the game, Gold subsequently pushed the silver horse down the a-file and took it hostage beside c3.
a b c d 8 7 6 5 4 game	Silver has blocked the gold camel, but Gold to move can still play a pull-and-replace with Ed6we hb6e Ha6e. Silver to move can prevent this by occupying the trap, but a silver piece on c6 might risk being flipped or pulled toward c3. In some cases, an EHD or EHH attack might aim to take b6 via a pull-and-replace while the attacker's camel is elsewhere.
a b c d 8 7 6 5 game	Gold plays Ec5we hb6s Ha6e. This pull-and-replace might seem easy, but it leaves d6 open for Silver. The silver camel might even come over and threaten to hostage the gold horse. If this pull-and-replace is not Gold's first priority, he might step his elephant to b5 with a threat to pull the silver horse on the next turn. If Silver could then move her own elephant to c5, however, Gold would have no viable threat here, and his elephant would be marginalized.
a b c d 8 7 6 5 game	The gold camel has just moved to c6, threatening to reach c7 or help the a6 horse onto b6. The advanced gold horse makes a western camel hostage unlikely. The camel is however vulnerable to a fork between c6 and f6; Silver can now play hb6n eb5n Mc6e eb6e, though the camel might then escape. If the silver elephant were more centralized, it might pull the camel out for a fork. An attacker in or behind a trap must beware of a fork, if its elephant is not between the traps. If the silver elephant leaves, the silver horse might be pushed toward c3.
a b c d 8 7 6 5 4 game	From this position the gold elephant occupied b6, pushing the defending horse away; the c4 gold horse then took b6 in what amounted to a multi-turn push-and-replace. A free silver camel could have punished the gold elephant's decentralization, but in this case the camels were deadlocked on the other wing.