Accelerated London System

The Accelerated London System is the move 2. Bf4 in the Indian Defense. White brings the dark-squared bishop out at once, so that the later e3, which supports d4, does not shut it in behind the pawns. The label "accelerated" reflects that the bishop appears before Nf3, the knight move that the London normally includes at an earlier point. Because 2. Bf4 is equally available after 1...d5, London players can use the same move against both of Black's main first replies.

White's scheme changes little from game to game: e3 and c3 to reinforce d4, Bd3, then Nf3 with the idea of Ne5, planting the knight on a central outpost. A more ambitious version puts the knight on c3 instead of playing c3, which leads to the Jobava-Rapport London. The play is mainly positional and depends more on understanding the set-up than on memorized lines.

After 2...d5 the game transposes to 1. d4 d5 2. Bf4 Nf6, where Black's usual third moves are ...c5 and ...e6. The point of this move order for Black, however, is that nothing has been committed in the center yet. In the Lichess database 2...g6 is the most frequent reply, aiming for a King's Indian-style arrangement with ...Bg7, ...d6 and ...c5, against which the Bf4 and e3 structure is less natural. 2...e6 and 2...d5 are each chosen about as often as one another, the former keeping both ...d5 and ...b6 in reserve. With 2...b6 Black adopts a Queen's Indian scheme of ...Bb7, ...e6, ...Be7 and ...d6, and combining ...g6 with ...b6 produces a double fianchetto. The sharpest try is 2...c5, when after 3. e3 Qb6 Black immediately attacks b2, a pawn that lost its defender when the bishop left c1.

The position ranks among the most commonly reached named openings, inside the top hundred of roughly 3,200, and it is especially widespread in online play. Results are close to level, with White scoring only slightly better than Black, and engines regard the position as roughly balanced, preferring 2...g6, 2...d5 and 2...e6.