The 'Battle of Murowana Oszmianka' was the largest clash between the Polish Armia Krajowa ('Home Army' resistance movement) and the Lithuanian Territorial Defence Force, a Lithuanian volunteer security force subordinated to the German occupational administration (13/14 May 1944).

The battle occurred in and near the village of Murowana Oszmianka in border region of Lithuania and Belorussia in the Generalbezirk 'Litauen' of the Reichskommissariat 'Ostland', and resulted in the routing of the 301^st Lithuanian Territorial Defence Force Battalion and, soon after this, the German disbandment of the entire Lithuanian force after its members had refused to take an oath of loyalty to Adolf Hitler and to agree to subordination to German commanders.

Late in April and early in May 1944, the Germans decided to transfer a significant part of the police duties in Lithuania to the newly created Lithuanian Territorial Defence Force, which was ordered to undertake a major anti-partisan operation against the Polish and Soviet partisans in the area. Three Lithuanian battalions were despatched to man garrisons in and around the town of Azmena. These battalions did not operate as complete units, however, for the SS demanded that they be dispersed as individual companies.

The Armia Krajowa commander for the Vilnius region was Aleksandr Krzyżanowski ('Wilk'), and he responded with the mobilisation of the region’s partisans. These were ordered not to engage the German-allied Lithuanian Territorial Defence Force lest any such action exacerbate Polish/Lithuanian hostilities.

While sending the battalions to the Vilnius region, the Lithuanian command secretly ordered the battalion commanders to avoid engagements with Polish partisans. Confident in their apparent superiority, however, the Lithuanian troops began to suppress the local Polish communities suspected of harbouring the partisans. Many war crimes were committed by the Lithuanian Territorial Defence Force, most notably the atrocities against Polish civilians in Paulava, Grauziskes and Sieńkowszczyzna. Faced with the need to protect Polish civilians, the Armia Krajowa decided early in May to fight back, and organised a concentrated assault against the Lithuanian fortified positions around the village of Murowana Oszmianka. On 10 May, Armia Krajowa units were ordered to prepare an assault against one of the larger Lithuanian Territorial Defence Force units in the region.

Major Czesław Dębicki ('Jarema') was chosen to command the five Armia Krajowa brigades (the 3^rd, 8^th, 9^th, 12^th and 13^th) that were to attack the LTDF positions in Murowana Oszmianka. Armia Krajowa reconnaissance established that the Lithuanian strength was was four companies of the 301^st Battalion in Murowana Oszmianka, which was the location of the Lithuanian local headquarters, two companies in Tołominowo, and a strong German garrison including armoured elements in Oszmiany. The strength and quality of the Lithuanian forces were ascertained to be superior by about 150 men, and this demanded the employment of a surprise attack to ensure a Polish victory.

On 12 May a detailed plan was created. It called for four platoons of the 8^th Brigade to attack Murowana Oszmianka from the south-east, converging on the church; the 3^rd Brigade to attack Murowana Oszmianka from the north-west; the 13^th Brigade to secure the road linking Murowana Oszmianka and Tołominowo, possibly attack Tołominowo, and prevent co-operation between the Lithuanian forces; and the 9^th Brigade to secure the road linking Murowana Oszmianka and Oszmiany. The bridge on the road linking Oszmiana and Murowana Oszmianka was to be blown up to prevent German armour from engaging in what became a significant Polish victory. Communication lines between between Vilnius and Oszmiana were to be severed. The 12^th Brigade and remaining cavalry platoon of the 8^th Brigade were to be held in reserve. A field hospital was to be established in the village of Wasiowce. Positions were to be taken at dusk, all units were to disengage by dawn to avoid a counterattack by German warplanes, and the attack was to begin at 23.00.

On the night of 13 May the 3^rd Brigade attacked the village from the west and north-west, while the 8^th and 12^th Brigades attacked from the south and east. The remainder of the Polish forces (13^th and 9^th Brigades) secured the road linking Murowana Oszmianka and Tołminowo road. The defences, reinforced with concrete bunkers and trenches, were manned by elements of the 1^st and 2^nd Companies of the 301^st Lithuanian Territorial Defence Force Battalion. This detachment was already wavering, however, following a defeat at Graużyszki on 5 May, where they had been dispersed by the 8^th and 12^th Brigades and suffered 47 casualties. The Polish assault was successful, partially as a result of the fact that other Lithuanian garrisons in nearby towns did not move from their positions to aid the forces in Murowana Oszmianka either directly or indirectly, the latter through attacks on other Polish elements. German reinforcements were stopped by the sabotage of bridges and delaying actions carried out primarily by the 9^th Brigade.

The 3^rd Company of the 301^st Lithuanian Territorial Defence Force Battalion was also engaged in the vicinity of the nearby village of Tołominowo by the 13^th Brigade. This engagement also ended in a decisive Polish victory.

During the fighting in Murowana Oszmianka and Tołminowo, the 301^st Lithuanian Territorial Defence Force Battalion was practically destroyed. Only its 4^th Company managed to evade the Polish forces and retreat. The Lithuanian Territorial Defence Force lost at least 50 men, with 60 more wounded and more than 300 taken prisoner: 117 of the prisoners were taken in Tołminowo. After the fighting had come to an end, all Lithuanian prisoners were disarmed (the Polish resistance forces thereby gained one mortar and seven machine guns) and released with only their underwear and helmets. The Lithuanian officers were given letters from Krzyżanowski, the Armia Krajowa commander in the Vilnius region, addressed to LTDF commander, General Povilas Plechavičius, appealing for an end to Lithuanian and German collaboration, an end to Lithuanian anti-Polish policies and a joint effort to combat the Germans. In response, the Lithuanians demanded that the Poles either abandon the Vilnius region, which was in dispute between Poles and Lithuanians, or subordinate themselves to the Lithuanians in their struggle against the Soviets. The Poles refused all these demands, and the Lithuanians refused to co-operate with them.

After their defeat in the 'Battle of Murowana Oszmianka' and other skirmishes with the Armia Krajowa, the Lithuanian Territorial Defence Force was found to have been weakened to the extent that Plechavičius and his officers were judged by the Germans to be useless, and were relieved of command. Soon after this, these officers were arrested and their organisation was dissolved.