In 1906, Jung built two 0-6-2T tank locomotives for the Ferrocarril Militar de Puente Alto al Volcán then under construction. It started in Puente Alto near Santiago at an altitude of 699 metres. The terminus at El Volcán at an altitude of 1,418 metres was 60 km away and was reached in 1914. The 600 mm gauge line was actually built to protect the border to Argentina, but also carried copper, gypsum, limestone and agricultural products.

The two locomotives had the works numbers 1306 and 1307 and got the running numbers 1 and 2. They weighed 17.1 tonnes in working order and had an output of 160 hp. The drivers had a diameter of 700 mm and the cylinders measured 300 by 350 mm. The trains often had one locomotive each on the front and the rear due to the steep incline.

The first one was named “Presidente Pedro Montt”, since it hauled the train that carried the president when the line was opened. The other one carried the name “Alberto Mackenna”. The third locomotive was an 0-6-0T built by Henschel and the fourth one was again similar to the first two, but built by O&K. Number 1 was withdrawn in 1957 and today is on static display at Puente Alto.