No one can say if Prayer helps a situation, but it's quite certain that it doesn't hurt.
I believe that God answers ALL prayers, however sometimes his answer is NO!
Did the Prayer that an Army Chaplain wrote for General Patton so he could have clear weather to liberate Bastogne Work? well the weather cleared early and the 101st Airborne was rescued. Power of Prayer? Who knows?
The Patton Prayer
Almighty and most merciful Father, we humbly beseech Thee, of Thy great goodness, to restrain these immoderate rains with which we have had to contend. Grant us fair weather for Battle. Graciously hearken to us as soldiers who call upon Thee that, armed with Thy power, we may advance from victory to victory, and crush the oppression and wickedness of our enemies and establish Thy justice among men and nations.