In February 1942, when AK was formed, it numbered about 100,000 members.[1] In the beginning of 1943, it had reached a strength of about 200,000.[4] In the summer of 1944 when Operation Tempest began, AK reached its highest membership numbers, though the estimates vary from 300,000[15] to 500,000.[16] The strength of the second largest resistance organization, Bataliony Chłopskie (Peasants' Battalions), can be estimated for summer 1944 (at which time they were mostly merged with AK[4]) at about 160,000 men.[17] The third largest group include NSZ (National Armed Forces) with approximately 70,000 men around 1943-1944; only small parts of that force were merged with AK.[10] At its height in 1944, the communist Armia Ludowa, which never merged with AK, numbered about 30,000 people.[7] One estimate for the summer 1944 strength of AK and its allies, including NSZ, gives its strength at 650,000.[1] Overall, the Polish resistance have often been described as the largest or one of the largest resistance organizations in World War II Europe.[a]