here is the description i got on it.
100% ORIGINAL & AUTHENTIC. VERY RARE! VERY GOOD CONDITION WW2 JAPANESE AIR DEFENSE FOOD RATIONS JAR. STATED ON THE JAR "DAI NIPPON AIR DEFENSE FOOD, PATENT VACUUM SEAL". IT IS ALL CERAMIC. THE TOP STATES TO HIT WITH A NAIL IN THE DEPRESSION TO OPEN, BREAKING THE VACUUM. THIS ONE WAS OBVIOUSLY OPENED DIFFERENTLY, MOST LIKELY WITH A KNIFE OR SCREWDRIVER BETWEEN THE TOP AND BOTTOM. I AM ASSUMING PEOPLE DID THAT IN ORDER TO TO REUSE THE CONTAINER. MEASURES 10 X 8.5 CENTIMETERS.