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xkcd #3119: Flettner Rotor
(imgs.xkcd.com)
Title text:
"And in maritime news, the Coast Guard is on the scene today after an apparent collision between two lighthouses."
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3119/
I'm pretty sure this is referencing the urban legend of a military vessel wanting a lighthouse to make way to them.