15 September 1916 – the first submarine to be sunk by an aircraft

On 15th September 1916, two Austro-Hungarian seaplanes sank the French submarine Foucault near the Bay of Kotor. It was the first time in history when a submarine was sunk by an aeroplane.

The Foucault (Q70) was a Laubeuf type submarine (Brumaire class) of the French Navy. The submarine was laid down on 1st November 1906 in Cherbourg, but construction works progressed slowly and she was launched only on 15th June 1912. Since the beginning of the Great War, the Foucault was part of the French Mediterranean Fleet.

Early in the morning of 15th September 1916, at the entrance to the Bay of Kotor, near Punta d´Ostro (now Rt Oštro in Croatia), the French submarine was spotted by Austro-Hungarian Lohner flying boat ´L132´, performing a patrol flight between Durazzo (now Durrës in Albania) and Kumbor (in today Montenegro).

Depending on source, there exist at least two versions regarding of crew of the L132 aircraft. The first one mentions Korvettenleutnant Dimitrije Konjović as pilot and Seekadett Maximilian Sewera as observer, but according to the second version, the crew was made of Sewera and Fregattenleutnant Walter Zelezny as the pilot.

The submarine spotted by the Austro-Hungarian crew was submerged but her silhouette was still well seen in clear waters of the bay. However, at that moment it was impossible to tell her navy affiliation. After the L132 arrival to Kumbor, Konjović – that held the position of the base commander – requested an information from the Austro-Hungarian Navy and, after receiving confirmation that no k.u.k. Kriegsmarine submarines were operating in that area, decided to attack the enemy.

The attack was performed by two Lohner seaplanes – the aforementioned L132 crewed by Konjović and Sewera; and the L135 with Zelezny and Fregattenleutenant Otto Freiherr von Klimburg. Both aircraft carried two depth charges and four conventional bombs.

The Foucault was near hit by at least two depth charges and got her engines, batteries and hull sealings damaged. The French thought the submarine entered a mine field, therefore the Foucault commander, Lieutenant de vaisseau Léon Henri Dévin, ordered the crew to surface the Foucault and then abandon the ship.

Unidentified French Brumaire-class submarine at Cherbourg (photo: Naval History and Heritage Command, Washington, DC – NH 55752)

On the surface, the surprised sailors realized they were attacked by two seaplanes. Initially, they opened machinegun fire on the aircraft but two more bombs dropped near the Foucault quickly dampened any actions and the submarine crew signalized their surrender.

Then, to another French surprise, the Lohner seaplanes landed near the submarine and picked up two French officers as POWs. The remaining twenty-six sailors were shortly after saved by an Austro-Hungarian torpedo boat. The Foucault sank shortly after being abandoned by the crew and thus became the first submarine in history to be sunk by an aircraft.

Dimitrije Konjović remained the Kumbor base commander until the end of the Great War. Then, he handed over the base and aircraft to Serbian authorities, and next joined the newly established Royal Yugoslav Armed Forces. Initially, Konjović was transferred to Novi Sad, the place he was born but later he was appointed the head of Maritime Aviation Department of the Royal Ministry of the Army and Navy.

After his retirement from the armed forces in 1923, Konjović was involved in creation of Ikarus aviation company and remained its shareholder for many years. After the Second World War, his properties and shares in the Ikarus company were confiscated by new Yugoslav government and Konjović focused on farming.

In 1968, the former Austro-Hungarian officer received an honorary diploma from the French government, in recognition of the humane way the sinking of the Foucault was performed – no one from the crew was injured and all sailors were successfully saved.

Dimitrije Konjović died in 1982, in Belgrade.

More information about the establishment of the Austro-Hungarian naval aviation can be found here, in our article issued in July of 2022.

Dimitrije Konjović (photo: Српска енциклопедија, CC BY-SA 4.0)

Cover photo: Lohner L flying boat, the same type as the L132 and the L135 that sank the Foucault. Source: Wikipedia Commons, public domain.
Sources: Hauke, Ervin; Schreder, Walter; Tötschinger, Bernhard: Die Flugzeuge der k.u.k. Luftfahrtruppe und Seeflieger 1914-1918 (1988) / Price, A: Aircraft versus Submarine (1973)