A World War II assault rifle that belonged to an SS officer was handed in to a gun buy-back organised by police in Connecticut.

The rare find, which is worth up to $40,000, would have been sent home by an American soldier who had taken it from a prisoner of war or a German he had killed.

Officer Lewis Crabtree, of the Hartford Police Dept, said: ‘The chance to see a piece of history – this – is absolutely unbelievable.’

Piece of history: The storm rifle is thought to be a Sturmgewehr 44, made in 1944 and issued to SS troops

Remarkable discovery: The gun was brought to the U.S. by an American soldier, who would have taken it from a German he had killed or taken prisoner

The gun was developed in 1944, holds a 30-round magazine and can shoot 500 rounds per minute.

It was handed in to the police by a woman on the first weekend of December, when they also collected 55 pistols, 91 revolvers, 13 rifles and two derringers.

As soon as they saw this weapon, officers realised it was something out of the ordinary, and agreed to allow the woman to sell it.

‘Usually, this rifle would be issued to SS troops,’ Officer Crabtree told NBCnews. ‘This is a gun that should actually be in a museum rather than in a shredder.

‘I give her credit for bringing it to us.’

His colleague John Cavanna, a gun historian, added: ‘In excellent condition, this gun is rated at $30,000 to $40,000.

‘You could kill a soldier back then, and if the captain of your fighting unit signed off on it, you could send that gun home to your family or kid brother or cousin.

‘[The seller’s] father, who was a World War II army man, had brought this gun home from the European theater.’

Every modern assault rifle produced today is based on this design, Officer Cavanna added.

Interesting detail: Officer John Cavanna, a gun historian, was thrilled to see the weapon, which he said was the basis for every modern-day assault rifle

THE STURMGEWEHR 44: WHY IS THIS GUN SO SPECIAL?

In battle: A photo of a German infantryman with a Sturmgewehr 44 in 1944, taken from the Federal Archives (Bundesarchiv) in Berlin

The gun found at this month’s buy-back is believed to be a StG 44 or Sturmgewehr 44 – literally ‘storm [or assault] rifle [model of 19]44’).

It was developed in Nazi Germany during World War II and was the first of its kind to see major deployment. It is now considered the first modern assault rifle by many historians.

Among the attachments available for the StG44 was the Krummlauf, a bent barrel that permitted firing around corners.

A trained soldier with a StG44 had an improved tactical repertoire, in that he could engage targets at longer ranges but still be effective in close combat, as well as providing covering fire like a light machine gun. The rifle was also found to be exceptionally reliable in the extreme cold of the Russian winter. Its rate of fire varied between 500 and 600 rpm.

A total of 425,977 StG 44s were produced by the end of the war, by which time a newer version was being made. Semi-automatic reproductions are still being made in Germany today.

It is unclear how many original StG 44s are left, although a cache of 5,000 were captured by Syrian rebels in the city of Aleppo in August of this year.