1. Kriegsspiel Map Making Template
Go to:
(military looking maps)
Or go to: (satellite/UAV looking maps)
Zoom into the area you want.
Take a screenshot (press the "PrtScn" button).
Go to: "View", "Slide Master" and navigate to the top level slide in the left hand box.
Paste the screenshot ("Ctrl-V" or right-click, "Paste")
Right-click on the image and "Send to back" (this lets the grid overlay the image). You can edit the grid numbers if you want to.
Re-size the image to get the scale correct with the 100m grid lines.
Use "Drawing Tools", "Crop" to remove unwanted stuff from the edges.
Use "Drawing Tools", "Corrections" to get the best colour contrast.
Close "Slide Master" and the map/grid will be the background.
You can now add any symbols, if you want to.

3. Example