Note from British ambassador Archibald C. Kerr to Vyacheslav Molotov with a personal and most secret message from Winston Churchill to Joseph Stalin on organising a meeting in Teheran
"I have been pondering about our meeting of Heads of Governments at Tehran. Good arrangements must be made for security in this somewhat loosely-controlled area. <...>
I suggest also that in all future correspondence on this subject we use the expression 'Cairo Three' instead of Tehran which should be buried and also that the code name for the operation should be 'Eureka'..."