Screenshots: http://imgur.com/a/WPVTm (link in comments)
This cannon will reliably sink the entire fleet in 4 shots, all the way from Wright Airport. Note that you have to spawn at Wright Airport. You probably also need a desktop or laptop with a high-res screen, I'm not sure whether you can even see the fleet from Wright Airport on a small screen.
Select air-to-ground mode to arm the cannon. The elevation is already set, you just need to traverse the gun (using 'roll') until the crosshair is right above a ship, then fire.