Complex sentence: America's greatest counterintelligence secret--in a locked safe in his office, choosing not to inform President Truman, Attorney General J. Howard McGrath, or Secretaries of State Dean Acheson and General George Marshall while they held office.
Split into simpler sentences: America's greatest counterintelligence secret--in a locked safe in his office. He choose to not inform President Truman, Attorney General J. Howard McGrath, or Secretaries of State Dean Acheson and General George Marshall while they held office.