|The Blackmar-Diemer Gambit is a chess opening that begins with 1. d4 d5 2. e4.|
An aggressive chess opening first explored by Armand Edward Blackmar, a relatively little known player in the late 19th century, but mostly advocated by the German master Emil Joseph Diemer (1908-1990). It was therefore named after these two players.
The Blackmar-Diemer Gambit is a true gambit in the sense that Black can hold on to the extra pawn if he so wishes. The accepted gambit usually continues 2...dxe4 3. Nc3 (the immediate 3. f3?! is not good as 3...e5! lets Black catch up in development) and now Black usually plays either 3...Nf6 or 3...Bf5. White will then continue with 4. f3, going permanently down a pawn but with good chances thanks to his superior development after 4...exf3 5. Nxf3 (5. Qxf3!? is also seen, see Halosar Trap).
Note that Black can also decline the gambit with 2...e6 (leading to a French Defense) or 2...c6 (leading to a Caro-Kann Defense). These are however less popular transpositions.
As with most gambits, White aims to achieve rapid development and active posting of his pieces in order to build up a rapid king attack. It is believed that Black is able to defend his position in all variations and consolidate his extra pawn to good chances in the endgame, so this opening is almost never seen in top-level play. It is however somewhat common in amateur play and a trusty weapon of many a club player.
Finally, presented here in algebraic chess notation is an example game that features the unusual feat of Grandmaster Efim Bogoljubov beating Diemer with his own favorite opening:
Bogoljubov - Diemer, Baden-Baden 1952:
1. d4 d5 2. e4 dxe4 3. Nc3 Nf6 4. f3 exf3 5. Nxf3 g6 6. Bg5 Bg7 7. Qd2 O-O
8. Bc4 Nc6 9. O-O-O a6 10. d5 Na5 11. Be2 b5 12. a3 Bg4 13. Ne5 Bxe2 14. Qxe2 Qd6 15. Rhe1 b4 16. axb4 Qxb4 17. Nd3 Qb6 18. Qxe7 Rab8 19. Na4 Qb5 20. Nc3 Qb6 21. Na4 Qd4 22. Ndc5 Nxd5 23. Rxd4 Nxe7 24. Rd7 Nf5 25. Nxa6 Rbe8 26. Rxe8 Rxe8 27. Nxc7 Re1+ 28. Rd1 Rxd1+ 29. Kxd1 Nc4 30. Nd5 Nxb2+ 31. Nxb2 Bxb2 32. Ke2 Be5 33. h3 h6 34. Ne7+ Kf8 35. Nxf5 hxg5 36. Ne3 Ke7 37. Kd3 f5 1-0