Cyfrinachau.
Davies, Helen Emanuel.
Lawrie, Robin.
Edwards, Meinir Wyn.
Talybont, Ceredigion : Y Lolfa,
2009.
Teitl clawr = Cover title.
Yn cynnwys mynegai = Includes index.
Fformat pen i waered, gyda stori un ochr a gwybodaeth ffeithiol yr ochr arall = Upside down format, with story on one side and factual information on other side.
World War, 1939-1945
Ciphers
Secrecy
Official secrets
Ciphers
Secrecy