Vowel Pawns (VP)

Definition:

1) a VP is a pawn that is, at one time or another of the game, in the file "a" or in the file "e";

2) a VP that leaves its file is no longer a VP (when capturing, for instance);

3) a regular pawn becomes a VP when capturing an opponent's unit on the "a" or "e" file;

4) a VP will never show on the 1st or on the 8th rank (a promotion turns a VP in another piece, for example);

5) at the start of an orthodox game, there are 4 VPs: the a2, a7, e2 and e7 pawns.

New rule:

The hereunder new rule is added to the orthodox chess rules:

« A game immediately ends by a "win" of side A when side A captures a VP or checkmates the King of side B ».

Question:

What is the shortest forced win by White against any Black defense?

Remark:

A VP is not a royal pawn, as those examples will explain. Orthodox play first: 

First White move: 1. Nf3 (orthodox play)

First Black move: 1. ... d5 (orthodox play)

Second White move: 2. Ne5 (orthodox play)

Illegal second move by Black  (orthodox play) as the King cannot put itself into check.

Now, what would be an illegal move in a game with royal VPs (which is NOT how we play here)?

Look at those moves (we put the star * after a move giving "check" to a royal pawn) :

First White move: 1. c3

First Black move: 1. ... b6

Second White move: 2. Qa4* (giving "check" to a7)

Second Black move: 2. ... Ba6* (giving "check" to e2)

The third White move is illegal here (royal VP variant): 3. h3

Why is this move illegal? Because the fairy royal condition stipulates 

that White cannot leave the pawn e2 "in check" and play elsewhere. 

(A royal VP, when threatened, behaves a bit like an orthodox King.)

Let's then take back 3. h3 and play the hereunder sound move instead:

Third legal White move (royal VP variant): 3. d3

The intended third Black move here would be illegal (royal VP variant): 3. ... Bxd3*

Why is this move illegal? Because the fairy royal condition says

that the above Black bishop a6 is pinned! 

The diagram below shows indeed such a pin in an orthodox game:

Orthodox game: the capture Bxe2 is illegal

Here is another example of how we treat "normal VPs" here.

After White's first move Nf3, it is absolutely legal for Black to play e5 (although suicidal): 

This move would be forbidden with royal pawns – but our pawns are not royal,

so we accept the legality of such a suicide

This is opposed to orthodox chess where the (suicidal) King's move we've seen already

is illegal (but this is the King, not a VP):

To make a long explanation short: VPs are not royal pawns!

This VP chess variant was posted a few days ago on the French forum France Échecs under the name "Pions-voyelles (PV)" – see here.

The shortest win for White happens on White's 10th moves (by sigloxx and pessoa, their proposal is below – and many thanks to sigloxx for correcting this page): but is it really the shortest one? I'm not sure that an "e3" opening by White fails in beating those 10 moves – though I couldn't find any solution in 9 or less... (Noam Elkies suggested that 1. c4 could be stronger than 1. c3 – who knows?)

[As before, the little star * below means "check to a VP"; the pair ** means "win by capturing a VP"]:

 1. c3      b6

 2. Qa4*    Ba6*

 3. d3      Nf6

 4. Bg5     e6

 5. Qd4     Bxd3*

 6. exd3    Nc6

 7. Qe3*    Ne4

 8. QxNe4*  Ne5

 9. QxNe5*   ~

10. Qxe6**

White's unstoppable threat after move #9