As a youth I was surprised to find a military map inside of an envelope in my uncle's 1950s military correspondence from Europe. Since then I have picked up several other examples from $1 boxes. Hard to show the inside without exploding the covers, but here goes ...
1. Used Feb 3, 1946, from APO 403 in Germany. American Red Cross on back flap. Map portion showing Cormery and Truyes, Indre-et-Loire department of France, near Tours, SW of Paris.



2. Used Feb 28, 1946, from APO 206 in Germany. American Red Cross on back flap. Map portion showing Janville Poinville, and Semouville, Eure-et-Loire department of France, SSW of Paris.



3. Used Apr 20, 1951, from APO 403 in Germany. Map portion showing Holtensen bei Wunstorf and Gross Munxel, west of Hanover, Germany.


4. Used May 15, 1952, from APO 403 in Germany. Map portion showing Vossmar east of Munster, Germany.


5. Used May 22, 1952, from APO 46 and postmarked at APO 162 in Germany. Large 8.5x11 envelope showing map portion of SW of Bremen including Furstenau and Ankum, Germany.


6. Used June 19, 1952, from APO 403 in Germany. Large 8.5x11 envelope showing map portion of "Muhldorf (E)" with Eggenfelden NE of Muhldorf, Germany.


7. Used Sep 5, 1952, from APO 403 in Germany. Map portion showing south end of Wassenburg, Bavaria, on the Inn River about 25 miles ESE of Munich, Germany.


8. Used July 2, 1957, from APO 30 in Morocco. Map portion showing Bernshausen on Seeburger Sea E of Gottingen, Germany.


9. Used Aug 17, 1957, from APO 113 Morocco. Map portion showing Wieda on the Wieda River SE of Hanover, Germany. previous collector exploded this cover, so we get to see all of it!


And the British did the same recycling with their old maps too.