Foggia became the major base of the 15th Air Force. Its 2,000 heavy bombers hit Germany from the south while the 4,000 heavies of the 8th Air Force used bases in Britain, along with 1,300 RAF heavies. While bad weather in the north often cancelled raids, sunny Italian skies allowed for more action. After that the Luftwaffe had only one success in Italy, a raid on the American port at Bari, in December 1943. Only 30 out of 100 bombers got through, but one hit an ammunition ship which was secretly carrying a stock of mustard gas for retaliatory use should the Germans initiate the use of gas. Clouds of American mustard gas caused over 2,000 Allied and civilian casualties.