The Navy apologized on Friday and said it has grounded an aircrew from Naval Air Station Whidbey Island, Washington, after its pilots drew a giant penis in the sky with jet exhaust on Thursday.

“The actions of this aircrew were wholly unacceptable and antithetical to Navy core values,” the Navy said in a statement. “We have grounded the aircrew and are conducting a thorough investigation—and we will hold those responsible accountable for their actions. The Navy apologizes for this irresponsible and immature act.”

“The Navy apologizes to anyone who was offended by this unacceptable action,” it added. “An investigation into this flight will be conducted and if appropriate, the aviator(s) responsible will be held accountable.”

On Thursday, pictures surfaced on social media of a penis drawn in the sky, prompting mostly amusement: