Nazi Germany operated around 1,000 prisoner-of-war camps () during World War II (1939-1945). Germany had signed the Third Geneva Convention of 1929, which established provisions relating to the treatment of prisoners of war. Article 10 required that PoWs should be lodged in adequately heated and lighted buildings where conditions were the same as for German troops. Articles 27-32 detailed the conditions of labour. Enlisted ranks were required to perform whatever labour they were asked if able to do, so long as it was not dangerous and did not support the German war-effort. Senior Non-commissioned officers (sergeants and above) were required to work only in a supervisory role. Commissioned officers were not required to work, although they could volunteer. The work performed was largely agricultural or industrial, ranging from coal- or potash-mining, stone quarrying, or work in saw mills, breweries, factories, railroad yards, and forests. PoWs hired out to military and civilian contractors were supposed to receive pay. The workers were also supposed to get at least one day a week of rest. Article 76 ensured that PoWs who died in captivity were honourably buried in marked graves. Types of Camps Dulag or Durchgangslager (transit camp) – These camps served as a collection point for POWs prior to reassignment. These camps were intelligence collection centers. Dulag Luft or Durchgangslager der Luftwaffe (transit camp of the Luftwaffe) – These were transit camps for Air Force POWs. The main Dulag Luft camp at Frankfurt was the principal collecting point for intelligence derived from Allied POW interrogation Heilag or Heimkehrerlager (repatriation camps) - Camps for the return of prisoners. Quite often these men had suffered disabling injuries. Ilag/Jlag or Internierungslager ("Internment camp") – These were civilian internment camps. Marlag or Marine-Lager ("Marine camp") – These were Navy personnel POW camps. Milag or Marine-Internierten-Lager ("Marine internment camp") – These were merchant seamen internment camps. Oflag or Offizier-Lager ("Officer camp") – These were POW camps for officers. Stalag or Stammlager ("Base camp") – These were enlisted personnel POW camps. Stalag Luft or Luftwaffe-Stammlager ("Luftwaffe base camp") – These were POW camps administered by the German Air Force for Allied aircrews. Nomenclature At the start of World War II, the German Army was divided into 17 military districts (Wehrkreis), which were each assigned Roman numerals. The camps were numbered according to the military district. A letter behind the Roman number marked individual Stalags in a military district.