Until the end of the war. Used primarily in the European campaign. The single star at distance by air crew was sometimes difficult to differentiate from german cross; especially American vehicles that can be easily confused with german (m18, m3, jeep) from the air. The term "American Luftwaffe" was coined. Circle is broken since a stencil was issued and many crews didn't bother to fill the gaps in. For the invasion of Sicily, crews were ordered to increase the width of the circle and paint it yellow.
Yes, some crews did away with it all together as it made a real easy target for german gunners.
