Double Fortress

The Double Fortress (相矢倉 or 相櫓 aiyagura) is a shogi opening in which both players construct Fortress formations.

Double Fortress
☖ pieces in hand: –
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香      桂香1
 飛 銀  金王 2
  桂歩 金銀歩歩3
 歩歩角歩歩歩  4
歩       歩5
  歩歩歩 歩歩 6
歩歩銀金 歩銀  7
 玉金角   飛 8
香桂     桂香9
☗ pieces in hand: –
Hifumi Katō vs Sōta Fujii 2016 after 38 moves[1]

Double Fortress games are the most common type of Fortress games found at all levels of play.

Historical Fortress

Earlier josekis for Fortress in the Edo period (usually spelled 櫓 at that time) were very different from the current josekis.

For instance, in one variation, it is White who delays pushing their rook pawn (whereas Black delays the rook pawn push in the modern era) and an early bishop trade occurs before both players' kings are moved into their castles.

In the 1947 Meijin tournament, Masao Tsukada and Yoshio Kimura played an early example of the typical 3. S-77 type of Fortress with 1.P-76 P-84 development found in modern shogi.[2]

Tsukada vs Kimura 1947
up to move 14
☖ pieces in hand: –
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香桂 金王金 桂香1
 飛 銀   角 2
歩 歩歩 歩銀歩歩3
    歩 歩  4
 歩     歩 5
  歩 歩    6
歩歩銀歩 歩歩 歩7
 角   銀 飛 8
香桂 金玉金 桂香9
☗ pieces in hand: –
1. P-76   P-84

2. S-78   P-34
3. S-77   S-62
4. P-26   S-42
5. P-25   S-33
6. S-48   P-85

7. P-56   P-54

1. P-76 P-84 development

3. S-77: Blocking bishop with silver
Fortress
up to move 5
☖ pieces in hand: –
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香桂銀金王金銀桂香1
 飛     角 2
歩 歩歩歩歩 歩歩3
 歩    歩  4
         5
  歩      6
歩歩銀歩歩歩歩歩歩7
 角    飛 8
香桂 金玉金銀桂香9
☗ pieces in hand: –
3. S-77

Blocking White's bishop with a silver (and also defending the eighth file from a possible attack) is an older Fortress joseki, which typically also includes advancing Black's rook pawn.

The more recent joseki advances Black's pawn on the sixth file instead. (See above.)

Classic Fortress 24-Move Set
Classic Fortress
up to move 24
☖ pieces in hand: –
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香桂   王角桂香1
 飛 銀金 金  2
歩  歩  銀歩歩3
 歩歩 歩歩歩  4
         5
  歩歩歩 歩歩 6
歩歩銀  歩  歩7
  金 金銀 飛 8
香桂角玉   桂香9
☗ pieces in hand: –

Classic Fortress 24-Move Set (旧矢倉24手組 kyū yagura nijū-tegumi)

Compared to the New Fortress 24-Move Set, note that the Classic Fortress 24-Move Set is (a) symmetrical where both sides have the same formation and (b) that only Black's formation differs (White's formation is the same in both the old and new josekis.)

Right Gold to 67 variant

Right Gold To 67 (6七金右 roku-nana kin migi)

Spearing the Sparrow
Spearing the Sparrow
up to move 25
☖ pieces in hand: –
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香桂   王角桂香1
 飛 銀金 金  2
歩  歩  銀歩歩3
 歩歩 歩歩歩  4
         5
  歩歩歩 歩歩歩6
歩歩銀  歩   7
  金 金銀 飛 8
香桂角玉   桂香9
☗ pieces in hand: –
25. P-16
Main article: Spearing the Sparrow

Spearing the Sparrow (雀刺し suzume-zashi)

3. P-66: Blocking bishop with pawn

At move 6, White also has an option to play Climbing Silver by advancing their rook pawn to rank 5. (See: White Climbing Silver.)

New Fortress 24-Move Set
Fortress
up to move 24
☖ pieces in hand: –
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香桂   王角桂香1
 飛 銀金 金  2
歩  歩  銀歩歩3
 歩歩 歩歩歩  4
         5
  歩歩歩 歩  6
歩歩銀金 歩 歩歩7
  金  銀 飛 8
香桂角玉   桂香9
☗ pieces in hand: –

New Fortress 24-Move Set (新矢倉24手組 shin yagura nijū-tegumi)

Quick Fortress castling
Fujii Quick castling
☖ pieces in hand: –
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香桂   王角桂香1
 飛 銀  金  2
歩  歩 金銀歩歩3
 歩歩 歩歩歩  4
       歩 5
  歩歩歩 歩  6
歩歩銀金 歩銀 歩7
   玉   飛 8
香桂角金  桂香9
☗ pieces in hand: –

Quick Fortress castling

White's Fortress Climbing Silver

Silver-37 variations

After the 24-move set of the Fortress opening, one major branch in the Fortress strategies is the Silver-37 set of variations. Many variations are under this parent variation.

Katō variation

Named after Hifumi Katō.

Waki System
Main article: Waki System

Morishita System
Main article: Morishita System

The Morishita System delays moving the right attacking silver to 37 early. Instead, it simply moves the bishop to 68 allowing the king to move into the Fortress castle in subsequent moves.

Other development patterns

1. P-76 P-34 2. P-66 patterns

Additionally, earlier Fortress openings in the first part of the 20th century did not follow from the standard 1. P-76 P-84 opening used today and instead developed from mutual opening of the bishop diagonals with 1. P-76 P-34.

Fortress development from Bishop Exchange

A Fortress position may also be developed from a rejected Bishop Exchange opening. For example, after a Bishop Exchange setup, instead of White trading the bishops off the board, White may choose to reject the bishop trade by closing their bishop diagonal. At this point, both players may convert their left side configurations into Fortress castles by pulling their bishops back and moving their silvers to the 77 and 33 squares. Thus, Black may move their bishop to 68 (or to 59 if their king moves to 69 first) allowing their left silver to move to 77. Likewise, White may move their bishop to 33 (usually triggered by Black pushing their rook pawn to 25), move their left silver to 22, move their bishop to 42 allowing their left silver to move 33.

Although possible, this Fortress development is not very common among professional players. When White rejects the bishop trade in this way, it is more common for White to play a Snowroof position while Black switches to a Fortress position instead of a Double Fortress game.[3]

Game example

Hirokazu Ueno vs Keiji Nishikawa 2008.[4]

gollark: Easy to parse would be... a HTML subset with less insanity, S-expressions, or JSON.
gollark: Observe my bad and experimental potatoprogram.
gollark: Because that would be very annoying.
gollark: Markdown is *quite hard* to parse, but it's parsed neatly and... not too ambiguously... to an AST.
gollark: minoteaur, eternally unfinished osmarksproject™ 5000, uses markdown.

See also

Bibliography
  • Aono, Teruichi (2009) [1983]. Better moves for better shogi. Translated by Fairbairn, John (2nd ed.). Ishi Press. ISBN 978-4-87187-999-6.
  • Aono, Teruichi (1983). Guide to shogi openings: Unlock the secrets of joseki 将棋定跡のカギ: 和英 定跡問題集. Translated by Fairbairn, John. 山海堂. ISBN 4-381-00598-8.CS1 maint: ref=harv (link)
  • Fairbairn, John (1981). "How to play the fortress opening part 1". Shogi (29): 4–6.
  • Fairbairn, John (1981). "How to play the fortress opening part 2". Shogi (30): 14–15.
  • Fairbairn, John (1984). Shogi for Beginners. Ishi Press. ISBN 978-4-8718-720-10.CS1 maint: ref=harv (link)
  • Hosking, Tony (1996). The art of shogi. The Shogi Foundation. ISBN 978-0-95310-890-9.CS1 maint: ref=harv (link)
  • Kitao, Madoka (2011). Joseki at a glance. Translated by Kawasaki, Tomohide. Nekomado. ISBN 978-4-9052-2501-0.CS1 maint: ref=harv (link)
  • Kitao, Madoka (2013). Sabaki at a glance. Translated by Kawasaki, Tomohide. Nekomado. ISBN 978-4-9052-2510-2.
  • "kieta senpō no nazo" 消えた戦法の謎 [Quest of the lost systems]. Shogi.Net. Mainichi Communications Co. 1995. · Partial translation of 消えた戦法の謎 kieta senpō no nazo by Kiyokazu Katsumata.
  • Yebisu, Miles (2016). Comprehensive shogi guide in English: How to play Japanese chess. Laboratory Publishing.
  • "ザ・雁木: ▲８八銀 ５六歩型の駒組み". 増田康宏の将棋講座. Episode 2. 2017. 銀河将棋チャンネル – via Niconico. (in Japanese)

References
  1. https://shogidb2.com/games/12aa48b21c47e76afd0b6b65bc0f28ab017f3a98
  2. https://shogidb2.com/games/201e12f1b4a87ad539354511f1569c0a7eeb38aa
  3. (ザ・雁木: Ep. 2)
  4. https://shogidb2.com/games/e375295892315770d4e97d34fcedd4495f6e5b87
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