For decades former Nazis and German war criminals served at the highest echelons of NATO.
Most of them were highly decorated Nazis, who later served in top positions in the Western German army, and were later promoted to serve as Commander and Chief of all NATO forces in Europe.
This was not a unique event, but a very common phenomenon in post WW2 western Europe and especially in Western Germany.
Nazi war criminals and people who supported and helped Hitler to carry out the holocaust and other war crimes, genocides and crimes against Humanity were almost never put on trial for their crimes against the Jews, the Poles, the Greeks, the Russians and the people of Europe, but instead were installed in top positions in NATO, in the western German government, army, industry and western German society at large.
The most famous of them was Adolf Heusinger, chief of the Operationsabteilung from 1940-1944. He was actually Hitler's chief of staff and helped plan the Nazi’s invasions of Poland, Norway, Denmark, and France. He was promoted to colonel on August 1, 1940 and became chief of the Operationsabteilung in October 1940, making him number three in the Army planning hierarchy.
After the war, this German war criminal, the man who helped Hitler plan and execute his invasion of neighboring countries which directly led to the deaths of millions of people, was not even put on trial, quite contrary he was allowed to take over the newly established West German army, the "Bundeswehr".
In 1961, Heusinger was made the Chairman of the NATO Military Committee (essentially he was NATO's chief of staff). He served in that capacity until 1964.
Heusinger was far from being the only Nazi war criminal who would later serve at a top position in NATO, here's a summary of a few more.
General Hans Speidel, a Nazi general who was Erwin Rommel’s chief of staff during WWII. After the war he served in the Western German army and became the Supreme Commander of NATO’s ground forces in Central Europe from 1957-1963.
Johannes Steinhoff, Luftwaffe fighter pilot during WWII and recipient of the Knights Cross of the Iron across (the Nazi military’s highest award), was Chairman of the NATO Military Committee 1971–1974 (among other NATO positions beforehand).
Johann von Kielmansegg (pictured left in first image), General Staff officer to the High Command of the Wehrmacht 1942-1944, was NATO's Commander in Chief of Allied Forces Central Europe 1967-1968.
Ernst Ferber, a Major in the Wehrmacht and group leader of the organizational department of the Supreme Command of the Army (Wehrmacht) from 1943-1945 and recipient of the Iron Cross 1st Class, was NATO's Commander in Chief of Allied Forces Central Europe from 1973-1975.
Karl Schnell, battery chief in the Western campaign in 1940/later First General Staff Officer of the LXXVI Panzer Corps in 1944 and recipient of the Iron Cross 2nd Class, was NATO's Commander in Chief of Allied Forces Central Europe from 1975-1977.
Franz Joseph Schulze, a Lieutenant in the reserve and Chief of the 3rd Battery of the Flak Storm Regiment 241 and recipient of the Knight's Cross of the Iron Cross in 1944, was NATO's Commander in Chief of Allied Forces Central Europe from 1977-1979.
Ferdinand von Senger und Etterlin; Lieutenant of 24th Panzer Division in the German 6th Army, participant in the Battle of Stalingrad, adjutant to Army High Command, and recipient of the German Cross in gold, was NATO's Commander in Chief of Allied Forces Central Europe 1979-1983.
Some people would say that some of these people were just army officers in a professional army and not war criminals.
However the Nazi Wehrmacht was not just a normal "professional army", it was an integral part of the German Nazi killing machine that was responsible for the deaths of 14 million civilians and the destruction of Europe and Western Russia.
Instead of facing trial for their particiaption in war crimes during WW2, they became top generals in NATO.