World War II: German forces begin a massive offensive against the <a href="https://en.wikipedia.org/wiki/Soviet_Union" id="mwxA" rel="mw:WikiLink" title="Soviet Union">Soviet Union</a> at the <a href="https://en.wikipedia.org/wiki/Battle_of_Kursk" id="mwxQ" rel="mw:WikiLink" title="Battle of Kursk">Battle of Kursk</a>, also known as Operation Citadel.