French Defense:Advance Variation, Milner-Barry Gambit

Named after Stuart Milner-Barry, the English player who was one of the codebreakers at Bletchley Park during the Second World War. White gives the d4 pawn for rapid development.

It is reached after 11 moves: 1. e4 e6 2. d4 d5 3. e5 c5 4. c3 Nc6 5. Nf3 Qb6 6. Bd3. It is a line of the French Defense.

Black is to move and has 35 legal moves. Over the next four moves — two for each side — the game can branch into 2,022,631 different games. Those games reach 630,277 different positions: most positions can be reached in more than one way, 3.2 on average.

The Lichess opening list names 4 further lines after this position, such as Hector Variation (6... cxd4 7. O-O) and Main Line (6... cxd4 7. cxd4 Bd7 8. O-O).

The same moves can be played in 6,000 different legal orders that all reach this position. For example 1. e4 e6 2. e5 d5 3. d4 c5 4. c3 Nc6 5. Nf3 Qb6 6. Bd3, which starts as the French Defense: Steinitz Attack.