The main resistance force in German-occupied Poland was the Armia Krajowa ("Home Army"; abbreviated "AK"). While AK command said it numbered 400,000 sworn members, only a very small fraction of these was involved in partisan warfare: in 1943 one percent and in 1944 possibly five to ten percent. Throughout most of the war, AK was one of the three largest resistance movements in the war. The AK coordinated its operations with the exiled Polish Government in London and its activity concentrated on sabotage, diversion and intelligence gathering. Its combat activity was low until 1943 as the army was avoiding suicidal warfare and preserved its very limited resources for later conflicts that sharply increased when the Nazi war machine started to crumble in the wake of the successes of the Red Army in the Eastern Front. Then the AK started a nationwide uprising (Operation Tempest) against Nazi forces. Before that, AK units carried out thousands of raids, intelligence operations, bombed hundreds of railway shipments, participated in many clashes and battles with the German police and Wehrmacht units and conducted tens of thousands of acts of sabotage against German industry The AK also conducted "punitive" operations to assassinate Gestapo officials responsible for Nazi terror. Following the 1941 German attack on the USSR, the AK assisted the Soviet Union's war effort by sabotaging the German advance into Soviet territory and provided intelligence on the deployment and movement of German forces. After 1943, its direct combat activity increased sharply. German losses to the Polish partisans averaged 850–1,700 per month in early 1944 compared to about 250–320 per month in 1942.