Censored Mail – WWII. 
Ireland was caught between a rock and a hard spot at the start of World War II. With the British and Germans starting hostilities in September 1939, the Irish were neutral but courted by both sides. The rulng Taoiseach, Edmund deValera (Figure 1) had no love for the British. Only his dual citizenship saved him from a British firing squad after the 1916 Rebellion. His nemesis, Winston Churchill (Figure 2) wanted to use Irish ports for convoys and warships to counter the German submarine threat. DeValera reasoned that if the British temporarily moved in military that it would be simple for the British to takeover on a permanent basis. On the other hand, the Germans threatened and bribed for access. In short, the decision was made for Ireland to remain neutral in spite of American pressure.
German espionage agents operated from Ireland, and encouraged the IRA to take action against the British. This was counter to the Irish government’s position. At the same time, many Irish nationals were in the British armed forces or worked in the defense industries. To prevent the British from using espionage as an excuse to invade Ireland, censorship of all inbound and outbound mail was begun by the Irish.
The pink resealing labels are known in nine different types. Figure 3. These were used on outbound mail to reseal envelopes after the ends were slit to allow the censors access to the contents. Verge identified the nine basic types and 18 more varieties in paper color, number format, and other variables. Figure 4.
Inbound mail was stamped with one of five different rubber stamps after scrutiny. Figure 5 is from a missionary in China which was exempt tfrom censorship.. Figure 6 is from a seaman aboard a British Navy ship. The “tombstone” marking is the Royal navy censor.
The English, in turn, examined all mail passing through their channels to and from Ireland including the British Northern Ireland. British resealing labels, the PC form 66 or the more common PC form 90 in label or tape format, often share space with Irish labels on outbound Irish mail.
Airmail from the US destined to Ireland arrived on the PanAm Clipper (Figure 7) at Foynes in the Shannon Estuary. The mail was transferred to Imperial Airline flying boats and taken to England for censorship, and then returned to Ireland afterwards. None of this made for good relations.
There were several air raids on Dublin and vicinity by the Luftwaffe, especially targeting train stations, and several were killed even though the Germain aircraft were operating at the extreme end of their operational radius.
It is unknown how effective the British censorship was. Irish citizens could travel freely between the countries by the ocean ferries, and carry messages if needed with relative immunity. Probably the perception of omnipotence put a halt to some subversive correspondence.
World War II censored mail has been studied extensively, and many articles and books address this multi-faceted area.
“The Irish S.P.1 Censor labels, 1939-1945” by C.J.G. Verge
“Censorship in Ireland in World War II”, Verge, C.J.G., The Revealer, Spring 1980, p.75ff.
“Censorship in Irish Mail in World War II”, Wollrect, Postal History Journal, No. 85, June 1990, p.32ff.
The operation of the Imperial (English) Censorship system has been covered in several books by the Civil Censorship Study Group.
The two volumes British Empire Civil Censorship Devices, World War II, United Kingdom by Konrad Morenweiser address how the operation was structured, the types and styles of resealing labels used, and the various details of the operation. This is supplemented by a censor number database on the Civil Censorship Study Group web site.
The final report by the British government, History of the Postal and Telegraph Censorship Department, 1938-1946 , Public Records Office, Kew, London, UK, Ref. DEFE 1/333, provides an insight of how senior management viewed the entire world-wide operation. This book is assumes the reader is familiar with the basic information, and is not easy reading.