Youth His parents were Kazimierz and Józefa Konstancja Kretschmer. He had two brothers, Stanisław and Tadeusz. He was raised in a family with patriotic traditions. He began his secondary school education in one of the Lviv gymnasiums. In the years 1908-1914 he continued his education in Jarosław. He studied at the local Imperial-Royal I Gymnasium, finishing the 7th grade in 1914. Before the outbreak of the
First World War, he was accepted to study at the Forestry Academy in
Vienna.
First World War After the outbreak of the First World War, he was sent to a reserve troop, which was later transformed into the 2nd Infantry Regiment. He was transported to Carpathian Ruthenia. On October 23, his unit fought its first skirmish with the Russian Army. On October 29, his unit fought in the
Battle of Mołotków, during which Stefan Mossor was wounded. On November 4, he shot himself in the hand and was delegated to serve as a telephone operator, and was then sent to hospital. On December 4, 1914, he joined the cavalry. In July 1915, he served in the 2nd Squadron of the 2nd Uhlan Regiment. On June 13, 1915, the squadron led a
charge near Rokitna. Then he went to
Rarańcza. In October, he was transferred to
Volhynia. During the first decade of November he served in the 3rd Regiment of the 2nd Brigade and took part in the battles of Lisów and
Kostiuchnówka. During one of the patrols he was injured or wounded and at the beginning of December 1915 he was hospitalized. On 10th February 1916 he was transferred to the Polish Legions in
Przemyśl. He was withdrawn to the frontline zone. On 10th October he arrived at
Baranavichy. After the announcement of the
Act of 5th November he made another journey to the
Congress Poland. On 12th March 1917 he was delegated to the 6th Squadron of the 2nd Uhlan Regiment. After the
oath crisis he remained in the ranks of the 2nd Uhlan Regiment. At the beginning of 1918 he was hospitalized. In February 1918 there was a mutiny, as a result of which Mossor was interned and sent to
Italy by the Austrians. According to the documents, he found himself in the town of Moline, was incorporated into the 6th Uhlan Regiment and commanded a platoon. In March, he received leave to
Jarosław. In August, he was sent to the cavalry officers' school in
Stockerau. The following month, he returned to his hometown. During the fights with the Ukrainians, he enlisted in a newly formed squadron and also broke through the village of Potylicz, occupied by the Ukrainians.
The Interwar Period After Poland regained independence, he served in the
Polish Army. In January 1919, he was promoted to officer rank. He was assigned to a full-time position in the 11th Uhlan Regiment located in
Mińsk Mazowiecki. He was then assigned to the
Blue Army under the command of General
Józef Haller. On July 7, he reported to the army headquarters and headquarters in
Kraków. In June, he began forming the 5th Siberian Division. During the
Polish-Soviet War, he commanded the 1st Squadron of the 4th Mounted Rifle Regiment. In 1921, he began his studies at the
Lviv Polytechnic. He was verified as a lieutenant and returned to the 6th Mounted Rifle Regiment in Hruszów. At the end of February, he applied for a transfer from the 6th Mounted Rifle Regiment to the 3rd Light Cavalry Regiment. On April 20 of the same year, he was assigned to a cavalry regiment. As a result of reorganization, Mossor ended up in Płock. On May 11, he became temporary deputy commander of the 2nd squadron. On January 17, 1922, he was transferred to the position of acting commander of the 3rd squadron. On August 3, 1922, he was promoted to captain. He was then delegated to the Central Cavalry School in
Grudziądz. In the years 1921–1927, he commanded a squadron in the 3rd Masovian Light Cavalry Regiment in
Suwałki. In the years 1927–1928, he was a student of the Higher Military School in
Warsaw. In 1928, after the first year of studies, he was sent to a two-year normal course at the École Supérieure de Guerre in
Paris. After completing his studies and obtaining the academic title of a
certified officer on November 1, 1930, he was assigned to the Higher Military Academy as a lecturer. In January 1934, he was transferred to the 10th Mounted Rifle Regiment in
Łańcut as deputy commander of the regiment. On September 15, 1935, he returned to the Higher Military Academy. In September 1937, Marshal
Edward Śmigły-Rydz, at the request of Gen.
Tadeusz Kutrzeba, assigned him to his staff as the first officer of the general's staff. From November 14, 1937 to January 10, 1938, under the direction of General Kutrzeba, he developed the Study of the Strategic Plan of the War Against Germany (the authorship is wrongly attributed to General Kutrzeba). On March 10, 1939, he was transferred from the staff position and took the position of commander of the 6th Mounted Rifle Regiment. On August 27 he was assigned to the
Łódź Army.
Second World War He took part in the
defensive war in 1939 as a lieutenant colonel and a commander of the 6th Horse Rifle Regiment. On September 11, he was taken prisoner by the Germans. He was sent to
Rawa Mazowiecka, and then to the camp in
Zgorzelec (Stalag VIII A). For the first month until mid-October, he served as the senior of block A. Then he was sent to camp II A in
Prenzlau. At the end of February 1941, he was transferred to Neubrandenburg. During his stay in the Oflag in Neubrandenburg, on April 17, 1943, together with a group of Polish officers, he was brought by the Germans to
Katyn, where mass graves of victims of the
Katyn massacre were discovered. There, he was introduced to the mass graves of Polish officers previously imprisoned in the camp in
Kozelsk. Than he prepared a report dated August 23, 1943, which he forwarded to the Commander-in-Chief. On June 11, he was transferred to Oflag 8 in Frauenberg near
Lübben. On August 4, 1943, he was sent to Neubrandenburgand in January 1944, he was transferred to
Oflag II D Gross-Born. To protect himself from accusations of collaboration with the Germans, he prepared and buried copies of the memoranda on the camp grounds. He was the last to leave the Gross-Born camp. ==After the War==