Aircraft such as the Blackburn Blackburn provide early warning by placing observers above the fleet. Patrols at roughly 1,000 to 2,000 feet, sometimes higher, can look out over 30 or 40 miles. Keeping at least one aircraft airborne extends the fleet's visual reach. Detection still depends on where an observer is looking, so an attack can approach from a direction that has escaped attention.
Notable Point · 50:35-51:33
Blackburn Blackburn patrols and visual early warning
Aircraft extend a fleet's visual warning range, but lookout height cannot remove the limitations of human attention.