Valkyrie (organisation)

Valkyrie was, according to the Twelfth Doctor, a conspiracy to remove Adolf Hitler from power during World War II. Erwin Rommel's opposition to Hitler led him to become involved in this. When the Nazis discovered this, they gave Rommel a choice — commit suicide or his family would be killed. Rommel chose to kill himself. (COMIC: The Instruments of War)

Behind the scenes
This appears to be a reference to the real-life Operation Valkyrie, which was an attempt to assassinate Hitler. However, Erwin Rommel was not involved in the real Operation Valkyrie, but a different plot.