United States. War Department, Dictionary of Spoken Russian — §7… (1945)
“ When nouns are compounded with пол- "half" they have the endings of the gs in the ns and as form; in all other case forms they have the usual endings, but пол- then optionally appears as полу-. Thus beside дюжина "dozen," as дюжину, gs дюжины, is дюжиной, there is полдюжины "half dozen," as полдюжины , gs полдюжины or полудюжины, is полдюжиной or полудюжиной, and so on. ”
