Flank Opening (Van Geet Opening)

1. Nc3 is an unusual opening that allows for a variety of transpositions, along with some independent lines.

Though it is a sensible move, developing a knight to a good square to control the centre, it is much less common than 1. Nf3. One reason is that the knight prevents White from playing c4, which they may be sad of if this transposes into a d4 opening. The other reason is that while 1. Nf3 prevents 1...e5, 1. Nc3 doesn't prevent 1...d5 (because after Black plays 1...d5, the d5 pawn is already defended by their queen).

In fact 1...d5 is the main response. 1...d5 threatens 2...d4 to take space and force White's knight to move again. There are some ways to prevent 2...d4: 2. d4 (transposing into a closed game); 2. Nf3 (transposing into a reversed Mexican defence); or 2. e3. However, it is most common to allow it with 2. e4, intending 2...d4 3. Nce2 e5 4. Ng3.

Several other moves allow White to play 2. e4 and transpose to a more common king's pawn opening, although there are ways of keeping the game in original territory.

1...c5 can transpose into the closed Sicilian defence if White plays 2. e4. Another line is 2. Nf3 Nc6 3. d4 cxd4 4. Nxd4, playing in the manner of a Sicilian defence but delaying actually committing the pawn to e4.

1...e5 invites a transposition to the Vienna game with 2. e4. If White wishes to avoid this, the main continuation is 2. Nf3 Nc6 3. d4, called the Napoleon attack.

1...Nf6 and 1...Nc6 are patient moves that pass the decision to play a pawn in the centre back to White. These may transpose into a line in the Vienna game if e4 & ...e5 are eventually played, or into a queen's pawn opening if d4 & ...d5.

This opening has a range of names, commonly Dunst for Ted Dunst (1907―1985) and van Geet for Dirk van Geet (1932―2012), and descriptive names queen's knight opening and Linkspringer (German: knight on the left). Its most poetic name is the Sleipnir opening, for Odin's eight-legged horse.

A historic game in this opening is attributed to chess amateur and Emperor of France, Napoleon Bonaparte, 1804.^[1]

Schiller & Benjamin cite FM Asa Hoffman as having "built most of his successful chess career on 1. Nc3", which they describe as "the best of the non-standard opening moves."^[2]

It is most often seen in blitz events where White is equally happy to play an e4 or d4 opening by transposition, and is letting Black choose.^[3]

1. Nc3

• Kasparov, Garry, & Keene, Raymond 1989 Batsford chess openings 2. ISBN 0-8050-3409-9.

• Nunn's Chess Openings. 1999. John Nunn (Editor), Graham Burgess, John Emms, Joe Gallagher. ISBN 1-8574-4221-0.

• Modern Chess Openings: MCO-14. 1999. Nick de Firmian, Walter Korn. ISBN 0-8129-3084-3.

Wikipedia has related information at Dunst Opening.