The US Navy has grounded one of its air crew after they used their advanced fighter jet to draw a penis in the sky.

The Navy E/A-18 Growler warplane flew in an unusual air pattern in the skies over Okanogan County in Washington state last week, using the condensed air trail from its exhaust to draw the giant phallic image.

Pictures of the reproductive organ suspended in the sky immediately went viral on social media.

The penis drawn by a US Navy air crew with the exhaust of an advanced fighter jet is seen in the skies over Okanogan County in Washington state (INSTAGRAM @RREED.69/via REUTERS)

The Navy, which is trying to crack down on sexual assault in its ranks, issued a formal apology for what it called an "irresponsible and immature act."

"Sophomoric and immature antics of a sexual nature have no place in Naval aviation today," Vice Admiral Mike Shoemaker, the commander of Naval Air Forces, said in a statement.