Pic of Osprey jogged memory that I woke to hearing one traveling east to west from the direction of Gowan Field, Boise, at about quarter past 1AM (MT).
VERY distinctive sound you'll never forget. Quieter in some ways than a Huey as they don't telegraph their approach with the whop whop whop of the helicopter, but a large volume of sound nonetheless. Very intimidating in squadron formation at speed. I think the sould says "your world is about to change". >>6830944