No Knights!

( A simple puzzle - with a difference - to illustrate a point. )

                   
8  
7  
6  
5  
4  
3  
2  
1  
    a b c d e f g h    

INTRODUCTION

This easy puzzle appeared in the February 2012 edition of E&T Magazine,
published by The Institution of Engineering & Technology.

I.E.T. was formerly the Institution of Electrical Engineers.
( I'm a Member. )

WHAT HAPPENED TO THE KNIGHTS?

The position shown could not arise with reasonable play but it is
possible after just six legal moves for each side.
Over to you.

( HINTS:  Use your chessboard.  Both sides must cooperate. )

•   •   ◊   •   •

Why am I showing you this rather trivial puzzle?

Well, normal chess puzzles ask you to play on from the position given.
This puzzle asks, "What happened in the past?"
It's a RETROGADE puzzle!

( More about this later. )

[ Answer to Previous Problem:  The Black Royalty is correctly positioned; White's King and Queen have swapped places! ]