UK codebreakers stumped by WWII pigeon message

"British intelligence officials are baffled by a secret World War II message that was discovered on the leg of a dead pigeon, they admitted on Friday."

"Codebreakers said the message, which did not include a date, was impossible to crack without its codebook."

The message:

AOAKN HVPKD FNFJW YIDDC
RQXSR DJHFP GOVFN MIAPX
PABUZ WYYNP CMPNW HJRZH
NLXKG MEMKK ONOIB AKEEQ
WAOTA RBQRH DJOFM TPZEH
LKXGH RGGHT JRZCQ FNKTQ
KLDTS FQIRW AOAKN 27 1525/6

[link to phys.org]