The title is referring to the Japanese Mitsubishi A6M Zero, a long range fighter aircraft operated from 1940 to 1945. At the beginning of World War II it was the combatant nations' best carrier based fighter, but new battlefield techniques and planes with more powerful engines surpassed the effectiveness of the Zero.
In this show after Parker shoots that Binghamton actually has lens in his glasses. During the series run Joe Flynn usually has lens free glasses.