BELGRADE, Nov 12 (Reuters) - Serbia has finally recalled to service as a floating museum a warship that fired the first shots that began World War One, following years of lobbying from navy ship enthusiasts who wanted it restored. The SMS Bodrog was one of two Austro-Hungarian heavy gunboats that sailed into the confluence of the rivers Sava and Danube around midnight on July 28, 1914. Its two canons hurled shells at Serbian positions in Belgrade, marking the start of the four-year war in which around 20 million people died. Renamed Sava, it also served in World War Two after it was taken over by Nazi German-ruled Croatia and was part of the former Yugoslavia"s navy until 1962 after which it was sold to a private company as a gravel barge. It was left to rot for years at its moorings near Belgrade after it was retired before the Serbian government granted it heritage protection status in 2005. "In 2015, the Defense Ministry decided that the ship should be placed under its auspices, it was added to the inventory of the Military Museum and over the next few years it has been restored and re-equipped," Natasa Tomic, a curator with the Belgrade-based Military Museum, told Reuters. Sava, which is now fully restored and floats on the river Sava near Belgrade"s city centre, is one of two surviving Austro-Hungarian river monitors which served during World War One. The other is SMS Leitha which is moored in Hungary"s capital Budapest. (This story corrects name of the river in last para to Sava, from Danube)