Backwards pawns

Part One: Reach the above position from the starting position

Part Two: Find the fastest way to get to this position.

Answering part one will get you an upvote, answering part two gets the checkmark!

• So for the record, is both colours allowed to be moved? And does both or only one king need to reach the other side? – Adam Mar 13 '19 at 18:28
• @Adam - This is called Retrograde analysis, and the standard constraint is that you are supposed to figure out how the position was arrived at via the normal rules of Chess - that is, alternating white and black moves, with white moving first, no unannounced checks, no failures to escape check, no illegal moves, and so on. – Jeff Zeitlin Mar 13 '19 at 18:50
• Also isn't the term "backwards pawn" a chess term? Lol – North Mar 13 '19 at 19:02
• @RewanDemontay it is not the same, unfortunately. See the link on your answer. – Brandon_J Mar 13 '19 at 19:42
• @North it is a chess term referring to a pawn that is too far back to be protected by the pawns on either side of it. – Brandon_J Mar 13 '19 at 19:44

Update: 28 moves!

Spoilers:

I couldn't solve the issue of wasted moves by W, so I reversed the polarity ;)

And another 29, where W is more efficient but in the end has to wait for B to catch up (W wastes 3 moves waiting).

• Great! Each pawn and knight only move twice, each bishop once three rooks twice and one rook once and the black queen only four times. That's as close to optimal as it is likely to get. I certainly can't see any wasted moves there. – Amorydai Mar 14 '19 at 22:12
• @Amorydai Actually I was unhappy with the three useless white Queen moves, and focusing on that I could get half a move better. – Arnaud Mortier Mar 14 '19 at 22:16
• Ah-ha! The improvement keeps coming. – Brandon_J Mar 14 '19 at 22:23
• @RewanDemontay With the strategy I had, it's quite possible. But there is a workaround :) – Arnaud Mortier Mar 15 '19 at 21:24
• @Brandon_J Yep, still coming :) – Arnaud Mortier Mar 15 '19 at 21:25

UPDATE: I got it down to

32 moves.

There's still some room for improvement, but it's the shortest one so far. Here's the link

• Looking good, looking good! – Brandon_J Mar 14 '19 at 2:06
• My best was 34. I'll wait a while to see if any better answers show up. If not, you have a check-mark coming your way! – Brandon_J Mar 14 '19 at 18:55

Legally:

Illegally:

16 moves if counted normally: 31 moves from standard set-up position into the layout in question (14 pawns to destination + 2 pawns outside, 12 other piece outside + 2 queens to position + 1 king out of check). Which is move each side both pawn except 2 (1 of each side to the outside of the board) and all other pieces except king and queen outside the board.

Credit to @Mukyuu for making the original game. I managed to get it down by half a move.

PGN viewer