Shock Troops features two extra pieces and 2 new pawns are available in reserve.

Instead of making a move, you can drop either the War Knight which leaps 1 or 2 spaces orthogonally or the Elephant Knight which jumps 1 or 2 spaces diagonally into the back rank.

You can also drop a Ninja Pawn into an empty space on second rank and optionally push it forward. Ninja Pawns move/capture like regular pawns, but also move 1 space laterally and capture 1 space horizontally on enemy half of board.

To drop a ninja pawn, click on its final destination square making sure that all the spaces from the original start square on the 2nd rank to this square are vacant.

For full details see: http://chess.computerwebservices.net/shocktroops.php