Anderssen Defense

The Anderssen Defense meets the Vienna Game with 2...Bc5, developing the king's bishop to its most active diagonal at once and pointing it at f2. Black delays committing the knights, so it remains open whether the game continues with ...d6, ...Nf6 or ...Nc6. It is considered an offbeat but playable alternative to the main replies, and José Raúl Capablanca chose it against Ilya Kan at Moscow 1936. The engine rates the position as roughly balanced, and in the Lichess sample White scores only slightly better than Black, with few draws.

3. Nf3 is by far the most common answer. Here 3...Nc6, transposing to the Three Knights Game, is inaccurate because of the fork trick 4. Nxe5 Nxe5 5. d4; after 5...Bd6 6. dxe5 Bxe5 7. Bd3 White has a large advantage. The reliable reply is 3...d6, holding e5 with a pawn. The main line continues 4. d4 exd4 5. Nxd4 Nf6, when 6. Be2 d5 7. e5 Ne4 8. O-O Nxc3 leads to equality. The sharper 6. Bg5 h6 7. Bh4 O-O 8. Nb3 is met in MCO-15 by 8...Bb4 9. Bd3 Re8 10. O-O Bxc3 11. bxc3 g5 12. Bg3 Nxe4, a sequence de Firmian assesses as giving Black at least equal chances. White can instead go for the bishop pair with the exchange line 4. Na4; after 4...Nd7 5. d3 Ngf6 6. Be2 O-O 7. O-O c6 8. Nxc5 Nxc5 9. Ne1 Ne6 10. c3 d5 the game is about level.

The second most popular move, 3. Bc4, transposes to the Classical Variation of the Bishop's Opening, where Black can choose among ...Nf6, ...Nc6 and ...d6. The delayed gambit 3. f4 is usually answered by 3...d6, reaching the Classical Variation of the King's Gambit Declined by transposition; of White's main tries, this one produces the best results for White in the database.

Two direct attempts to exploit the bishop are rare and unsound. The Giraffe Attack, 3. Qg4, runs into 3...Nf6 4. Qxg7 Rg8 5. Qh6 Bxf2+, after which 6. Kxf2 loses the queen to 6...Ng4+; Black obtained a large advantage this way in Tsikhelashvili–Karpov, USSR 1968. The Hamppe-Meitner Variation, 3. Na4, chases the bishop with a knight on the rim before White has developed anything else. Black can reply 3...Bxf2+ 4. Kxf2 Qh4+ 5. Ke3 Qf4+ 6. Kd3 d5, with wild complications in Black's favor, as in the Immortal Draw, Hamppe–Meitner, Vienna 1872. The calm retreat 3...Be7 also gives Black a good game.