what does the red mean?

[v0031]

Whatever the rationale, sending Zeroes to the Aleutians would prove to be a critical intelligence error for Japan. On June 4, with orders to bomb the Allied base Dutch Harbor on Unalaska Island, young pilot Tadayoshi Koga, thought to have been 19 years old, strapped himself into his plane and prepared to carry out the mission of the Imperial Army. Little is known about Koga. In an undated service photo, he looks directly into the camera, almost smiling, his left hand tucked into the pocket of his uniform. Confident? Definitely. Perhaps even showing a bit of swagger. But then, what Japanese pilot wouldn’t swagger with the indomitable Zero at his command?
When Koga took off for Dutch Harbor that June morning, he probably expected to complete his mission and return to base as usual. Things didn’t work out that way. Emerging from the ubiquitous fog that envelopes the entire Aleutian Islands chain five or six days a week, Koga acquired his target and strafed the enemy base. During the engagement, his plane took ground fire that severed its main oil line. Now, piloting a fighter trailing a stream of oil, Koga realized that the moment the last drop of lubricant spilled out, his plane’s engine would seize and his Zero would plummet to earth.

[Grumpier Than Uncle Joe]

The guys on the ground were shooting at the plane and they shot and severed (cut) his oil line doing so.