The discovery of a grenade dating from the War of Independence in Dublin's Grand Canal close to Harold's Cross bridge made headlines last summer. However, as Lar Joye, Port Heritage Director at Dublin Port, and former curator of the Military Collections at the National Museum, explained to Myles Dungan on RTÉ Radio 1's History Show, there are probably plenty of other munitions from Ireland's revolutionary years still out there in a variety of places. Here are some lightly edited extracts from that discussion

"If you look over the last four or five years, this is happening maybe two or three times a year, quite spectacularly also in some of the rivers", explained Joye. "A grenade was found in Ballsbridge in 2017 and if you're on the internet, you'll see some very dramatic footage of it being exploded by the bomb squad near the bridge in Ballsbridge. Many of them are, of course, a legacy of the War of Independence and the Civil War when they were very, very prevalent. Even since then, I suspect some have been thrown into the canal to be got rid of. So, it has become a very, very common event over the last couple of years."

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From RTÉ One's Six One News, report on a War of Independence and Civil War exhibition at the National Museum at Collins Barracks

The Grand Canal grenade was a Mills' bomb, the distinctive pineapple-type grenade seen in countless war movies over the years. "That's the one invented by a gentleman called Mills in 1915 and millions and millions were in use in the British Army right up into the 1960s", explained Joye.

"It was a very effective weapon when you threw it and took between four and six seconds to explode and had a killing range of about 20 metres circular around the explosion so quite an effective and nasty piece of equipment. That's why even today they have to be treated with some safety. They are very dangerous as they're designed to do one thing. So if you do ever find one, make sure that you don't touch it, and contact the relevant authorities."

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From RTÉ Archives, Tom Barry's memories of the Kilmichael ambush in Co Cork in 1920

Most of the munitions found from the War Of Independence would originally have come from the Crown Forces' arsenal. "The British Army, they're the ones that are going to have these grenades", says Joye. "When you look at, say, the Kilmichael ambush, when you look at the equipment list set out by Tom Barry after the ambush, they're all carrying one or two grenades, as well as revolvers and rifles. They're very, very well equipped. And in an ambush situation, grenades and throwing grenades are the ideal thing to have.

"The IRA themselves, of course, wouldn't have access to this kind of mass-produced weapon so they make a big effort to make the steel casings for the grenades. You'll find these casings which were made in places like the Inchicore Railway Works even today in the National Museum and other museums and also in small foundries all over the country, quite easy to make for anyone involved in steelworks.

"However, the difficulty for the IRA was the explosive material. Looking for gelignite was a big thing in 1919. But also trying to import explosives from England and then smuggled onto the various ferries coming into Dublin. Many of the times when you look at the various ambushes that occur, especially in 1920 and into 1921, grenades are thrown, but they might necessarily explode so you're going to have a dud for whatever reason. Sometimes the explosive doesn't work. Sometimes the fuse doesn't work. In Kilmichael, Tom Barry starts the ambush with a grenade, which does go off."

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From RTÉ One's Six Onew News, report on a trove of War of Independence papersand medals saved from a skip in Co Clare

The Crown Forces left Ireland in 1922 so why didn't they take all their grenades with them? The reason why we are still finding them dumped in rivers and canals, believes Joye, is down to quartermasters dealing with paperwork. "I always have a suspicion that quartermasters were clearing out their stores in 1922 and having maybe too many grenades that don't match what it says on paper so came up with a solution of getting rid of excess grenades that weren't officially on the books. The best thing to do is get rid of the excess and just dump them or get rid of them."

Joye gives the example of grenades found about 20 years ago in the National Museum in Collins Barracks during some building work. "The bomb squad were called in and then they were taken away and later on disposed of. It would be nice to know the history of these grenades and to find out if they have serial numbers, and do the history, if you like, of them or the archeology of them. However, you're never fully sure what state they are when they're found so safety is the dominant thing here. They're taken away and then a controlled explosion occurs because you can never take the risk. You can't just leave a grenade on a shelf and hope nothing will happen."

Hand grenades on display in the Curragh Military Museum, Co Kildare in 1977. Photo: RTÉ Stills Library

Joye reckons there's not that many illegal guns and rifles out there. "Being an Island nation, trying to get a gun into the country was difficult enough for the IRA. Illegal collections of weapons are rare enough. These grenades are turning up because the canals are an easy way of getting rid of them. In 1919 and 1920, anyone who held a gun license had the gun taken off them and the weapon put into storage. Something similar happened in 1972 at the beginning of the Troubles so there's been these regular intake of weapons from around Ireland.

"If you go back into the 19th century, the first gun licenses were introduced in Ireland as an experiment by the British government even before gun licenses were introduced in England. Gun ownership in Ireland for illegal guns has been well monitored. Searches have been carried out even for legal guns. If you look at the history books, a lot of the famous Thompson machine guns that came in from America in the 1920s, a lot of those were recovered in big, large arms dumps in 1942 and 1943 so a lot of this stuff has already been taken up.

You can hear the interview in full below

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