Commander
Leader, Fuhrer
noun, suffix
The commander of the whole army is just called " the commander." No one knows his real name and everyone is too afraid to ask.
そうすい
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
それは、ヒトラー総帥の指令だったのです。
That was Fuhrer Hitler’s order.