When the F-35 flies over friendly countries for overseas deployments, you may notice some strange tags on the body of the otherwise sleek jet.

F-35 lunebergWhat are those? Lockheed Martin

Every angle and surface of the F-35 has been precisely machined to baffle radar waves, so little notches like the ones on the picture above would defeat the purpose of the weapons system that has cost about $400 billion so far.

Here’s the Marine Corps‘ F-35B flying clean:

f-35b uss america f 35 marine corpsAn F-35Bs taking off from the USS America. Lockheed Martin

The notches, which are called Luneberg reflectors, serve a purpose. The reflectors increase the F-35’s radar signature several hundred times over so that a plane that would normally be nearly impossible for civilian air traffic controllers to spot would give off a big, safe blip.

Perhaps the F-35B above didn’t need the reflectors because it took off from the sea, away from potential spotters.