Wernher Von Braun once said.....

Your sentence corrected:
Wernher Von Braun once said that if he had been given the chance to decide whether or not to join the Nazi party, he would have refused.

My alternative: (note: 'von' is usually spelled with a small 'v')
Wernher von Braun once said that if he had been allowed to choose whether to join the Nazi party, he would have refused.

I would add that von Braun joined Nazi party in 1937. He was offered, by Himmler in 1940, the chance to join the SS. He accepted because his boss, Dornberger, said he had "absolutely no alternative" if he wanted to continue his rocket work. Although he maintained that this, like his party membership was purely "on paper", he wore his uniform regularly to official meetings, was promoted three times and ended the war as an SS-Sturmbannführer.

On the other hand, von Braun was under SD surveillance from October 1943. He had expressed regret that he was not working on a spaceship and that he felt the war was not going well; this was considered a "defeatist" attitude. He was later arrested by the Gestapo but released on Hitler's orders because of his importance to the war effort.

On the other hand, von Braun was under SD surveillance from October 1943.

My question is this:

What does "SD" stand for or is short for?

Thanks again for the help.

The Sicherheitsdienst (full title Sicherheitsdienst des Reichsführers-SS) or SD was the intelligence agency of the SS and the Nazi Party.