A series of underground tunnels used by Michael Collins to test submachine guns during the War of Independence is now open to the public.

The interconnecting chambers and tunnels run underneath the grounds surrounding the Casino at Marino on Dublin’s north side, and a new exhibition at the site is exploring the tunnels’ historical significance, the Irish Times reports.

The tunnels were originally excavated by James Caulfeild, 1st Earl of Charlemont, who hired Scottish architect Sir William Chambers to build the Neo-Classical structure on his grounds in the 18th century. 

Some of the underground chambers were designed as bathing pools

“He would take a constitutional in his parkland, and then go underground to one of his grottos to restore his constitution with cold water,” said Pauline Kennedy, supervisor guide at the Casino.

The purpose of the other chambers and tunnels is unclear.

“We don’t know conclusively what they were all used for,” said Kennedy. “There are lots of different theories. But tunnels always excite the imagination.”

The tunnels were probably intended to connect to the Marino House, but the Earl ran out of money before the project could be completed. He died bankrupt in 1799.

Around May 1921, Volunteers from F Company of the Dublin Brigade used the longest tunnel, which runs almost to the perimeter of the grounds, to practice firing the first two Thompson submachine guns that had arrived into Ireland from fundraising efforts by Harry Boland in the U.S.

According to witness statements, soon after the guns arrived, Michael Collins, Oscar Traynor, Richard Mulcahy, Ginger O’Connell and other rebel leaders used the tunnel for firing practice.

“We had heard stories that Michael Collins had used our long tunnel to practice firing,” said Kennedy. “And we knew that the Mauser rifles and ammunition unloaded from the Asgard in Howth in 1914 had probably been stored here. With that background of revolutionary activity, I went trawling through the Bureau of Military History archives.” 

Kennedy said she found several witness statements confirming that many of the revolutionary leaders had used the tunnels for firing practice.

For more information visit casinomarino.ie.