The 'Jabłonków Incident' was an event on the border between Poland and Slovakia in which a group of Abwehr military intelligence agents attacked a railway station in Mosty (25/28 August 1939).

The main purpose of this German undertaking was to capture the Jablunkov pass and its strategically important railway tunnel, and then to hold it until relief by a larger German force. The attackers were repelled by units of the Polish army, however, and the incident is regarded as a prelude to Germany’s Weiss' (i) invasion of Poland. The 'Jabłonków Incident' is usually reckoned as the first commando operation of World War II.

The start of 'Weiss' (i) was initially scheduled, according to Adolf Hitler’s order, for 04.45 on 26 August, but on the day before this the launch of the full-scale invasion was postponed as, on that day, Hitler learned that the UK had signed a new treaty with Poland, in which British military support for Poland was offered if Poland was attacked.

Part of Germany’s 'Weiss' (i) plan involved the commitment of small groups of Germans dressed in inconspicuous but rugged 'Räuberzivil' (robbers' civvies) to crossings of the border the night before and seizing key strategic points before dawn on the day of the invasion. The secret Abwehr battalion detailed to undertake these operations was what became Bau-Lehr-Bataillon zbV 800 (800^th Construction Training Company for Special Duties) on 15 December 1939. A group under the command of Leutnant Dr Hans-Albrecht Herzner of the Abwehrstelle 'Breslau' was instructed to facilitate the imminent advance of Generalmajor Eugen Ott’s 7^th Division by infiltrating the border region. The men of this special force were to capture the railway station at Mosty in the Jabłonków pass in the Carpathian mountains in order to prevent the destruction of the single-track railway tunnel which provided the shortest connection between Warsaw and Vienna.

The Jabłonków pass, which separates mountain ranges of Moravian-Silesian Beskids and the Silesian Beskids, is one of the most important transport routes through the western part of the Carpathian mountains. In October 1938, together with the territory of Zaolzie, it had been annexed by Poland in the aftermath of the Munich Agreement, so Poland thus controlled a key railroad connection, the railway line between Kosice and Bohumín. The rail tunnel and the station at Jabłonków were part of the line. The Germans knew that any failure to capture the line and the tunnel would be a serious blow to the movement of German forces in southern Poland.

The task of Herzner’s Abwehr detachment was thus to take and hold the station at Mosty and the tunnel to prevent the latter’s destruction by Polish forces. The detachment was ordered to occupy the Jabłonków pass before the start of hostilities started. Within this overall objective, the The Germans were to disable possible Polish demolition systems and to open the way for the advance of the 7^th Division from Munich.

The headquarters of the Polish army was fully aware of the strategic importance of the tunnel, and as a result this was prepared for demolition as early as June 1939 by the 21^st Sapper Battalion from Bielsko, under the command of a reserve officer, Pułkownik Witold Pirszel, who was a mining engineer. The tunnel was guarded by men of the border guards' local post in Świerczynowiec, and an infantry platoon of the 4^th Regiment of Podhale Rifles. The nearest national defence base was at Trzyniec. On every day in the summer of 1939, after the passage of the last train Polish sappers armed the explosive charges for the night at each end of the 985-ft (300-m) tunnel.

The German detachment of some 70 or, according to some sources, 24 men in civilian clothes left Čadca late in the evening of 25 August. During the night, they crossed the Polish/Slovak border near Velký Polom mountain to reach the station at Mosty at about 04.00 on 26 August unaware that Hitler had cancelled his order and delayed the start of the invasion of Poland until 1 September. The Germans took up positions on a hill near Mosty station and began to fire on the station building, as well as at a house where the principal of a local Polish school lived. In the minutes which followed, the Germans captured the station after some fighting, and took prisoner a group of workers on their way to the Třinec iron and steel works. However, the German unit did not know that the station was equipped with a military communication system, located in the basement, and from this a female telephonist managed to call Polish units guarding the tunnel, and the alarm was raised. Polish sentries armed with machine guns took positions at each end of the tunnel and established an observation post. There followed a chaotic exchange of fire, after which the Germans realised that the operation was a failure and scattered into the nearby woods. Some attackers managed to capture a locomotive and tried to enter the tunnel, but were repelled by Polish police. The Germans remained under heavy fire while trying to withdraw into Slovakia, and finally managed to extricate themselves at about 12.00 on 26 August, with two wounded.

After the incident Ott, commander of the 7^th Division, which was concentrated in the area of Zilina, apologised to General brygady Józef Kustroń, commander of the 21^st Mountain Division stationed nearby and responsible for border protection. Ott claimed that the action had been staged by an 'insane' individual, who was acting entirely on his own initiative.

The tunnel in Jabłonków was blown by Pukownik Witold Pirszel at 06.00 on 1 September, 75 minutes after the German army launched 'Weiss' (i), and just a few minutes before German troops arrived. Rail communication was restored partially in February 1940, and wholly in 1941.