It was the period between 1933-1943 that saw the original SMERSH's most active overseas operations. During this period, the "Main Enemy" of all Soviet activities was the British Empire. Thus, MI5 and MI6 were the primary opponents of GRU-SMERSH during the period. The methods utilized by MI5 and MI6 and their effectiveness were of particular concern to the GRU and helped increase the paranoia of the Stalinist regime. Thus, few successful SMERSH operations were conducted in the British Empire.
In the United States, as the GRU organized ARMTOG was the sole representative of Soviet power, SMERSH's primary opponent in North America was the Federal Bureau of Investigation. However, while the FBI was effective and surveillencing many communist operations they were as yet unaware of the larger strategic outlines of Soviet operations and thus were often caught off-guard by SMERSH's assassination squads. Thus, many of SMERSH's most successful executions occurred in the United States and Latin America and not Western Europe. They coordinated the assassinations of thousands of suspected Soviet agents that were believed to have turned ranging from Harold Ware in 1935 to Leon Trotsky in 1936 and Juliet Stuart Poyntz in 1937.
The documented cases of suspected SMERSH assassinations outside of the Soviet Union run in the hundreds if not thousands. However, the full extent of the homicides committed by SMERSH overseas will never be known. But given the rather brutal nature of communist party work in covert activities and the highly dangerous world of military human intelligence operations let alone the context of espionage in nations wracked by civil war like China and Spain and Colombia, the numbers are not shocking.
As World War II brought the US, UK, and USSR into alliance, the focus of Soviet counter-intelligence shifted. Thus, during the war the main opponent of SMERSH in its counterintelligence activity was Abwehr, the German military foreign information and counterintelligence department, active during both World War I and World War II.
In all of these operations against foreign intelligence services, SMERSH operated at a more complex and subtle environment and its activities were then part of a larger and more coordinated 'maskirovka' (masked operation) which included the full apparatus of the Soviet organs. Although, SMERSH was utilized as a killing instrument in operations against the Germans, British, and Americans and other powers, it was usually done so as a subordinate agent rather than the principle agent of Soviet activities.
Activity domestically and on the Eastern Front
Since the writ of SMERSH was targeted against traitors, the Soviet Union's national security organs were structured as a counter-intelligence apparatus, and SMERSH primarily originated as a battlefield counter-intelligence group, it was at home in the military ranks that most large scale activities of SMERSH were conducted.
Organized principally to carry out special activities against dissidents within the military including wiping out mutineers, a close look at another vile and brutal Soviet tactic is instructive: the Punishment Battalion. Each military regiment had attached to it a punishment battalion. This military unit's sole role was establish a behind the edge of the battle field area of operation from which all dissidence to the Soviet Union was eliminated. This area was the province of anti-partisan, anti-sabeteur, anti-espionage activities on the battlefield by GRU.
Additionally, the punishment battalions other activities in securing this area was establishing a killing zone in which even Soviet troops were killed if they fled the battlefield. Used only in extraordinary circumstances, the punishment battalions would begin forcing Soviet soldiers forward to ensure they didn't break upon assaults on the enemy or flee from a defensive position when assaulted. Investigating potential mutineers or those who refused to properly implement orders and then carrying out their executions in this area was the final role of SMERSH.
As Soviet armies began their advance upon occupied German territory, it was foreseen that a substantial period of insurgency against Soviet arms would begin. Most of the Ukrainian and a substantial portion of the Belorussian population was opposed to the Soviet Union. Large armies had in fact been recruited by the Germans to aid in their war against the Soviets at the front and in the rear against the Red Partisans. To secure the supply lines, effect military order, and establish Soviet power it was viewed necessary to utterly smash any opposition or dissidence to Soviet rule. Therefore, it was concluded that SMERSH needed to be reinforced with substantial new assets including legal standing within the Soviet power structure. It was these new requirement which caused the previously shadowy SMERSH to come out from clandestine operations under military service commands to strategic authority under Stalin's direct command.
SMERSH activities also included "filtering" the soldiers recovered from captivity. It was also used extensively to "filter" the population of the gained territories, including Eastern Europe. The SMERSH was directly involved in the collection, interrogation, and execution of tens of thousands of Polish military officers, clerics, and political leaders at the Katyn Forest Massacre. The SMERSH was also actively involved in the capture, of tens if not hundreds of thousands of suspected disloyalists, anti-Soviets, and White Partisans in the Soviet Union such as forced repatriation, and execution of Soviet citizens who had been active in anti-communist armed groups fighting on the side of Nazi Germany such as the Russian Liberation Army, the Cossack Corps of Pyotr Krasnov, and the Organization of Ukrainian Nationalists. This also included eastern POWs and eastern workers. Finally, SMERSH handled the capture and interrogations and executions of hundreds of thousands of German and Japanese POWs as well as the capture of thousands of American, British, French and Chinese soldiers, sailors, airmen, and expatriates many of whom were later murdered or died in captivity.
SMERSH was also used to punish those within the NKVD itself; it was allowed to investigate whomever it wished in the NKVD structure; department and directorate heads were not immune from it. Smersh would also often be sent out to find and kill defectors, double agents, etc.
SMERSH was also used by INO (the NKVD's later KGB FCD, First Chief Directorate, responsible for foreign intelligence operations outside of the USSR) to hunt down "enemies of the people" outside of Soviet territory.
As the war concluded, SMERSH was given the assignment of finding Adolf Hitler and, if possible, capturing him alive or recovering his body. Red Army officers and SMERSH agents found Hitler's partially burned corpse near the Führerbunker after his suicide and conducted an investigation to confirm the events of his death and identify the remains which (along with those of Eva Braun) were reportedly secretly buried at SMERSH headquarters in Magdeburg until April 1970, when they were exhumed, completely cremated, and dumped in a river.