French Defense, Rubinstein Variation, Fort Knox Variation

The Fort Knox is commonly reached by 1.e4 e6 2.d4 d5 3.Nc3 dxe4 4.Nxe4 Bd7 5.Nf3 Bc6. It can also arise after 3.Nd2. Black exchanges the d5-pawn for White's e4-pawn early and then reroutes the c8-bishop through d7 to c6.

The sequence is written in algebraic notation: squares such as e4 combine a column letter and row number; N means knight, B bishop, R rook, and Q queen; pawn moves normally show their destination, x marks a capture, and + marks check. Moves are read in pairs, White first and Black second; dots before a move shown alone indicate Black's turn.

That route addresses a familiar French Defense problem: the c8-bishop can be restricted by Black's own e6-pawn. A bishop limited by its own pawns is often called a bad bishop. In the Fort Knox, Black brings that bishop out before completing a compact setup: the b8-knight goes to d7, the g8-knight to f6, the f8-bishop to e7, and short castling places the king on g8 and rook on f8.

The positional balance

• Black obtains pawns that are hard to attack, few immediate weak squares, and opportunities to exchange pieces so White's attacking force is reduced.
• White usually controls more central squares, can bring the pieces out easily, and has time to prepare c4, Bd3, Qe2, or pressure against the center.

The name does not mean the position is impossible to break. If Black only defends, White can build pressure gradually. Black must choose the right moment for ...c5, a pawn advance that attacks White's center and opens lines, or for exchanges of active pieces. The Steinitz Variation keeps more pawns in the center and creates a different struggle, although both require Black to challenge d4, which often supports White's center.