The Irgun operated a sophisticated recruitment and military-training regime. Those wishing to join had to find and make contact with a member, meaning only those who personally knew a member or were persistent could find their way in. Once contact had been established, a meeting was set up with the three-member selection committee at a safe-house, where the recruit was interviewed in a darkened room, with the committee either positioned behind a screen, or with a flashlight shone into the recruit's eyes. The interviewers asked basic biographical questions, and then asked a series of questions designed to weed out romantics and adventurers and those who had not seriously contemplated the potential sacrifices. Those selected attended a four-month series of indoctrination seminars in groups of five to ten, where they were taught the Irgun's ideology and the code of conduct it expected of its members. These seminars also had another purpose - to weed out the impatient and those of flawed purpose who had gotten past the selection interview. Then, members were introduced to other members, were taught the locations of safe-houses, and given military training. Irgun recruits trained with firearms, hand grenades, and were taught how to conduct combined attacks on targets. Arms handling and tactics courses were given in clandestine training camps, while practice shooting took place in the desert or by the sea. Eventually, separate training camps were established for heavy-weapons training. The most rigorous course was the explosives course for bomb-makers, which lasted a year. The British authorities believed that some Irgun members enlisted in the Jewish section of the Palestine Police Force for a year as part of their training, during which they also passed intelligence. In addition to the Irgun's sophisticated training program, many Irgun members were veterans of the Haganah (including the Palmach), the British Armed Forces, and Jewish partisan groups that had waged guerrilla warfare in Nazi-occupied Europe, thus bringing significant military training and combat experience into the organization. The Irgun also operated a course for its intelligence operatives, in which recruits were taught espionage, cryptography, and analysis techniques.