A smertnik (Russian: смертник, lit. 'condemned man') was an infantryman of the Imperial Japanese Army that launched suicide attacks against Soviet armored columns. It was a pejorative used by Red Army personnel during the Soviet invasion of Manchuria (August 1945).

Japanese–Soviet relations had been somewhat stable throughout most of World War II. In April 1941, the Soviet Union and the Japanese Empire signed a neutrality treaty that held even after the June 1941 invasion of the Soviet Union by Japan's key European partner, Nazi Germany. This invasion also prevented the Soviet Union from helping the Western Allies fight Japan after the attack on Pearl Harbor on 7 December 1941. Soviet leader Joseph Stalin also believed that Japan would continue to expand southwards and thus away from the USSR, reducing the urgency of committing Soviet troops against Japan. After tentative promises at the 1943 Moscow Conference to Cordell Hull and W. A. Harriman that the USSR would enter the war against Japan once Germany was defeated, Stalin made a full commitment to Winston Churchill and Franklin Roosevelt at the Tehran Conference later that year.

After the German surrender on 8/9 May 1945, the Red Army began moving troops to bolster its forces in the Far East. Shortly after midnight on 9 August 1945, Soviet forces attacked across their own country's border into Manchukuo, a puppet state of the Japanese Empire.

Several Japanese suicidal ground attacks had occurred before August 1945, such as during the Battle of Kakazu Ridge [ja] and the Battle of Okinawa.

An example of anti-tank suicide attacks by Japanese tanks occurred in April 1945, towards the end of the Battle of Luzon. As Allied forces advanced upon Baguio, where the headquarters of the 14th Area Army were located, a Japanese general^[which?] ordered the three remaining tanks of the 5th Company, 10th Tank Regiment – a tank unit directly under the command of the headquarters – to halt the advance of the United States Army tank units, which consisted primarily of M4 "Shermans."

Pursuant to this order, company commander Lieutenant Takao Sakurai formed a tank-based suicide unit to ram and repel the U.S. tanks. Sakurai ordered First Lieutenant Niwa and eleven other personnel to form a tank suicide squadron comprising one Type 95 Ha-Go light tank and one Type 97 Chi-Ha medium tank. These two tanks bore an unusual appearance, each fitted with a protruding rod extending 1 metre from the front, tipped with 20 kg of explosives. Furthermore, the four tank crew members who could not fit inside the two tanks were to conduct tank dismounting, two per vehicle. These dismounted crew members each carried a duffel bag filled with depth charges and several hand grenades slung from their waists, intending to carry out a human wave assault by ramming the enemy vehicles. The tank suicide squad, divided between Niwa's two tanks, advanced to Ilisan near Baguio after being seen off by Army Commander Tomoyuki Yamashita. There, they camouflaged their tanks and lay in wait for the American tank column. At 9:00 am on the 17th, Niwa's camouflaged tank unit launched a surprise attack on an American Army M4 medium tank approaching a bend 200 metres northwest of the Ilisan Bridge. Startled by the sudden appearance, the lead American tank missteered and plunged 50 metres down a cliff. The two Niwa tanks then charged to ram the following vehicles. An M4's gunfire struck the turret of Niwa's Type 95 Light Tank, blowing it off, but undeterred, the two Japanese tanks rammed the M4s head-on. The tank crew members, who had been conducting a tank dismount, jumped from the tanks just before the collision. As the tanks charged, they rammed the M4 medium tanks. Surviving Japanese tank crew members threw grenades at American tank crew members attempting to escape from the M4 medium tanks or drew their swords and charged in to slash at them.

Both sides' four tanks exploded and burned, their wreckage obstructing the American tank column's route of advance. As the roads near Ilisan were narrow, removal of the wreckage was difficult. The US Army was delayed for about a week, during which time the Baguio headquarters was able to withdraw in an orderly manner, along with large numbers of wounded and military supplies. Japanese official war histories refer to this as the "tank headbutt".

Japanese infantry had neither sufficient artillery, such as rapid-fire guns and long-range field guns, nor infantry-portable anti-tank equipment, comparable to the American Bazooka, German Panzerfaust, and British PIAT, to halt the large number of tanks deployed by Allied forces. Consequently, the Japanese were compelled to devise methods for close combat against tanks. Various forms of anti-tank suicide attacks were employed, but the standard-issue close-quarters tactic involved attaching the Type 99 mine to a tank's armour plate and detonating it. Japanese infantrymen would close in on enemy tanks carrying the Type 99 Anti-Tank Grenade. They would magnetically attach it to the hull, pull the safety pin from the fuse section, and strike the head. The grenade would then detonate approximately five seconds later. It could also be thrown like a hand grenade. When successfully adhered to armour plates, a single grenade offered only about 20mm penetration, and even two stacked grenades provided merely 30mm penetration – hardly devastating. However, this proved sufficient against light tanks. In Burma alone, six M3A3 tanks were confirmed destroyed within a single month. An analysis by the US Army Intelligence Department stated: "In light of recent combat experience in Burma, this report on damage caused by the Type 99 Anti-Armour Grenade clearly indicates that this weapon will become one of the principal threats to Allied tanks posed by Japanese forces." Furthermore, the Anti-Armour Grenade was also employed by the Giretsu Airborne Unit during their assault on airfields in Okinawa, proving effective in destroying aircraft.