Puzzle of the week #119

Level: 
4-Rook
Chess Diagram: 

----rrk-
----Qppp
p--P-n--
-p------
---p----
PB------
-PP---Pq
-K-RR---

"The enemy is at the gates". Have you heard this expression before? It means a critical moment has been reached, a moment when talk is no more useful. It is for sure a moment of tough decisions. The attacker must decide how to attack (retreating is not an option...), doing its best to keep sacrifices at minimum but not forgetting the final goal: winning! It is your turn to be the general of the White army in the above position. You are at the gates. What will you do?
a) White to move and win;
b) Explain your solution.

Total available points for this puzzle is 20. The answers will be published next week together with puzzle #120.

Puzzle #118 solution:
Our puzzle appeared in Boy's Life magazine from Dec 1966. Fischer comment at the time was: "It's a rough one that will take some thought". It is interesting to note half of you got it, while the other half did not. I had 3 best answers to choose from, so here it comes my selection: Karl's answer. However it could have been any other one as well.
"1.Bd8! ...
This move was actually found by logical random testing. At first, I tried using the Rook in many ways, but it didn't work. Next I tried my King and that didn't work either. My basic idea for this move is to limit the Black King's movement by cutting off c7 and e7. There are 3 lines here. Most would respond:
1... Kxd8
2.Kd6 ...

Moving the rook here would result in Black's King coming back up.
If 2... Kc8 3.Rb2 Kd8 4.Rb8#
If 2... Ke8 3.Rf2 Kd8 4.Rf8#
Now the other 2 lines go like this:
1... Ke8
The king tries escaping through the side, but it's no use.
2.Ke6 Kf8
3.Rg2 Ke8
4.Rf8#

Or:
1... Kc8
Black tries to run the other way because our Rook can't come to a2 like it could go to h2 in the previous line.
2.Kc6 Kb8
3.Bb6 ...

Black is trapped on the back rank. White mates next move with Rd8#. Note how using the Bishop wouldn't work in the previous line because Black can escape on the h-file.
The key to this puzzle is to keep the Black King's space limited, so he can't run so many ways. With the Bishop sacrifice, White was able to stop it from escaping, or dragging the game on."

Correct solutions:
Andy Y, Owen, Karl - 20 points
Jeffrey - 15 points
Frank, Edwin - 10 points
James, Nathaniel, Alex - 8 points

STANDINGS

Owen - 358 points
Andy Y - 355 points
Karl - 338 points
Edwin - 301 points
Jeffrey - 256 points
Andy Q - 214 points
Alex, James - 207 points
Humphrey - 180 points
Nathaniel - 144 points
Amir - 103 points
Frank - 30 points
Rick - 18 points
Marko - 10 points

Comment: 

The enemy is at the gates