amass arms and military equipment abroad for transfer to Palestine once the British blockade was lifted. In the United States, Yishuv agents purchased three Boeing B-17 Flying Fortress bombers, one of which bombed Cairo in July 1948, some Curtiss C-46 Commando transport planes, and dozens of half-tracks, which were repainted and defined as "agricultural equipment". In Western Europe, Haganah agents amassed fifty 65mm French mountain guns, twelve 120mm mortars, ten H-35 light tanks, and a large number of half-tracks. By mid-May or thereabouts the Yishuv had purchased from Czechoslovakia 25 Avia S-199 fighters (an inferior version of the Messerschmitt Bf 109), 200 heavy machine guns, 5,021 light machine guns, 24,500 rifles, and 52 million rounds of ammunition, enough to equip all units, but short of heavy arms. The airborne arms smuggling missions from Czechoslovakia were codenamed Operation Balak. The airborne smuggling missions were carried out by mostly American aviators – Jews and non-Jews – led by ex-U.S. Air Transport Command flight engineer Al Schwimmer. Schwimmer's operation also included recruiting and training fighter pilots such as Lou Lenart, commander of the first Israeli air assault against the Arabs. Arms production The Yishuv also had "a relatively advanced arms producing capacity", that between October 1947 and July 1948" produced 3 million 9 mm bullets, 150,000 Mills grenades, 16,000 submachine guns (Sten Guns) and 210 three-inch (76 mm) mortars", along with a few "Davidka" mortars, which had been indigenously designed and produced. They were inaccurate but had a spectacularly loud explosion that demoralised the enemy. A large amount of the munitions used by the Israelis came from the Ayalon Institute, a clandestine bullet factory underneath kibbutz Ayalon, which produced about 2.5 million bullets for Sten guns. The munitions produced by the Ayalon Institute were said to have been the only supply that was not in shortage during the war. Locally produced explosives were also plentiful. After Israel's independence, these clandestine arms manufacturing operations no longer had to be concealed, and were moved above ground. All of the Haganah's weapons-manufacturing was centralised and later became Israel Military Industries. Manpower In November 1947, the Haganah was an underground paramilitary force that had existed as a highly organised, national force, since the Arab riots of 1920–21, and throughout the riots of 1929, Great Uprising of 1936–39, and World War II. It had a mobile force, the HISH, which had 2,000 full-time fighters (men and women) and