The find (see gallery) came during building cleanup work at the national police museum.

Uno Trumm, a researcher at the Virumaa museums foundation, said: "The police museum started organizing the base of its eastern chimney on the second floor, and among the heaps of soot, debris, and other waste, two mortars suddenly emerged."

The museum acquired the mortars, likely dating to World War One, for its collection about a hundred years ago. Most probably, with the Soviet and Nazi occupations of Estonia starting in 1940, museum staff concealed the weapons – thought originally to total four, with two likely lost for good.

Trumm said: "We had inventory lists of the items we had, and two mortars were missing. They weren't found, and that was that."

"It was wartime; things could disappear anywhere. The Nazis actively collected scrap metal in 1942 and 1943, so it was also possible that they were taken as scrap metal," he went on.

"In December 1929, Defense Minister Oskar Köster issued an order giving a whole collection of weapons to the Rakvere museum, thus opening its weapons department," he added, explaining how the mortars came to be there in the first place.

Period barbed wire was also found among the debris during the cleanup work.

Estonian War Museum researcher: Findings are a 58 mm F. R. mortar and a 47 mm Lihhonin mortar.

Siim Õismaa, a researcher at the Estonian War Museum, assisted ERR in identifying the mortars, stating both were used by the Russian army.

He said: "In general, large-caliber mortars used by the Russian army were not considered the safest, and most of those left in storage after the [Estonian] War of Independence were decommissioned and given to museums for exhibitions or placed in barracks as decorations. The remaining ammunition after the War of Independence was destroyed for safety reasons."

The French 58 mm mortar was designed during World War I under the leadership of artillery general Jean Dumézil.

The Russian army adopted it in 1915. "The second type was 20 cm taller than the first, with a longer and wider carriage and twice the weight," said Õismaa.

While a French development the mortars were also produced in the Russian Empire, including in Tallinn.

Over 3,400 F. R.-type mortars were built across the Tsarist empire.

The type was used by Estonian infantry during the War of Independence. The mortar fired several types of over-caliber projectiles and was likely built in Tallinn at the Baltic Shipyard.

Meanwhile the 47 mm Lihhonin mortar was designed in 1915 by Russian military engineer Captain Yevgeny Lihhonin. By the end of World War I, 767 units had been produced at the Izhora Steel Plant.

Only a few of these mortars were in Estonia during and after the War of Independence, no more than ten. It is unclear to what extent they were deployed in combat situations.

Editor's note: This article was updated to include information on identification of the mortar types.

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