Ireland War code notes with ETO code.
In neutral Ireland the war era was termed "The Emergency". This is reflected in the A Series notes of the era which were produced with a special marking in the form of an overprint—the Emergency Tracer Overprint code—a letter in a circle on the top left and bottom right of each banknote for all denominations except the £50 and £100 notes.
The ETO codes (also called war codes) were used on Ten Shilling notes and five Pound notes dated from 1940 to 1944, and on all denominations from 1941 to 1944.
The ETO war code was an extra security feature, used to keep track of the Irish banknotes from the time of their production in England to their being delivered safely to Ireland. The usage of ETO codes on Irish notes commenced in September 1940 when the Blitz started and ceased after the D-Day landings in 1944, when German bombing of London had stopped.
These are my favorite notes.
There is a section on the main web site devoted entirely to ETO war code
There are 26 letter combinations.
All denominations are easily available, except the £20 note which is rare.
Central Bank of Ireland War code 20 Pounds Specimen 1943
Central Bank of Ireland War code 10 Pounds 1943
Central Bank of Ireland 5 Pounds Specimen War code 1943
Currency Commission Ireland One Pound War code 1941 T
Central Bank of Ireland 10 shillings War code Specimen 1943