U-29, built by the Hungarian firm of Ganz Danubius at Fiume, was launched in October 1916 and commissioned in January 1917.

During her service career, U-29 sank three ships and damaged one warship, sending a combined tonnage of 14,784 to the bottom.

[3][Note 2] After these steps alleviated their most urgent needs,[6] the Austro-Hungarian Navy selected the German Type UB II design for its newest submarines in mid 1915.

[3] Although there is no specific notation of a range for U-29 in Conway's All the World's Fighting Ships 1906–1921, the German UB II boats, upon which the U-27 class was based, had a range of over 6,000 nautical miles (11,000 km) at 5 knots (9.3 km/h) surfaced, and 45 nautical miles (83 km) at 4 knots (7.4 km/h) submerged.

[3] After intricate political negotiations to allocate production of the class between Austrian and Hungarian firms,[8] U-27 was ordered from Ganz Danubius on 12 October 1915.

Departing Brgulje on the 25th to resume her journey to the Mediterranean, the submarine developed a leak when performing a test dive.

[2] Prásil took U-29 out of Cattaro on 17 February to begin the delayed patrol in the Mediterranean, but on the 20th encountered another severe storm.

The beleaguered U-boat headed back to the base at Pula for more repairs, and remained there until early April.

[2] While 25 nautical miles (46 km) from Cape Matapan, Prásil torpedoed and sank the steamer Dalton, traveling in ballast.

[12] Five days later and some 115 nautical miles (213 km) away, U-29 torpedoed Mashobra, a British India Line passenger steamer of 8,173 GRT.

The ship, en route from Calcutta to London with a general cargo, was finished off by U-29's deck gun.

After eleven days at sea, Prásil torpedoed the British cargo ship Mordenwood 90 nautical miles (170 km) from Cape Matapan.

[16] Escorting destroyers launched a depth charge attack on U-29 but did not succeed in damaging the U-boat.

Two days later, U-29 launched a torpedo attack on the British steamer Marie Suzanne but did not sink the ship.

One day out, the U-boat came under attack from an airplane out of Valona, compelling U-29 to crash dive; none of the three bombs dropped by the aircraft hit their mark.

After a return to Pola on 12 July, the U-boat underwent extensive repairs that kept her out of action for the next nine months.

Near Valona the next day, an Italian destroyer attempted to ram U-29, scraping one of her propellers against U-29's conning tower.

The Allied escorts (mainly American submarine chasers) subjected U-29 to a heavy depth charge attack.

Josef Guenther Lettenmaier, who served on U 29 as "Maschinenquartiermeister", roughly equivalent to Machinist Mate 2nd Class, documented his experiences in the Austro-Hungarian Navy and aboard U 29 as historical fiction in "Rot-Weiss-Rot zur See", published by Tyrolia Verlag, Innsbruck, 1934.