The flash of the explosion was seen miles out to sea and the blast was heard 20 miles away. It was 3am on September 21st, 1917, and most of the citizens of Arklow were asleep. But the night shift of 200 men and 12 girls at the Kynoch munitions factories which stretched for over a mile along the Co Wicklow shore line were hard at work making explosives for use on the battle fronts of the first World War.

They were mixing nitro-glycerine and gun cotton in four isolated huts. Some said later they heard a whirring sound before it happened. When it did happen three of the huts vanished completely. Windows were shattered over a wide area, and townspeople living nearby were thrown from their beds. At the factory up to 28 workers vanished with the huts and many more were injured. They were treated at the factory’s small hospital on the site of what is now the Arklow Bay Hotel. Exact details of the incident were rapidly smothered by wartime censorship and it could not be ascertained with certainty just how many people perished. Some historians say 17, others 28. There is no argument that had the explosion occurred during the day shift the toll of dead and injured would have been much higher.

Rigid social and security structures were imposed on Arklow to facilitate the operation of the factory, which at its peak employed up to 5,000 people. Armed police and British soldiers guarded the entrances around the clock. Local pubs had restricted opening hours to deter excessive drinking. Every publican had to provide accommodation for at least three soldiers. Workers had to wear wooden clogs in the factory to prevent sparks. (Clogg Lane, where they were manufactured, remains to this day near the hotel). Fishing boats could not leave port during the hours of darkness and had to fish at least five miles off shore. Coastguard families had to leave their cottages to accommodate the military.

The celebrated artist George Campbell, more commonly associated with the Belfast of his upbringing than the Arklow of his birth, claimed the explosion was the genesis of his migraine attacks. He was born near the scene of the explosion at St Patrick’s Terrace on July 29th, 1917, and was convinced the explosion of the following September had impacted in some way on his first tender formative months. Earlier this year the local council in Arklow unveiled a commemorative plaque at Campbell’s birthplace. An exhibition of his paintings runs at the Arklow public library until the end of the month.

The munitions plant at Arklow was established by George Kynoch, a Scottish entrepreneur, around 1894, but the driving force was the chairman of the board, Arthur Chamberlain, a Birmingham industrialist and uncle of Neville Chamberlain, who was the British prime minister in 1939 when Europe descended into another World War. It initially employed 260 men, women and teenage boys and girls.

The men were paid 12 shillings a week, about average at the time, but the women got only four shillings. There were a number of fatal accidents and several industrial disputes about pay and conditions. The factory hospital recorded 900 injuries, many from acid burns, and, according to the Wicklow People, some men were incapacitated for life by noxious fumes.

Production was boosted by the demands of the Boer War in South Africa but that rise was dwarfed by the needs of the ever-gaping guns in Belgium and France in the war to end all wars. During a visit in September 1915 John Redmond, the leader of the Irish Parliamentary Party at Westminster, congratulated the workers on “helping to save existing civilisation from German ruthlessness.”

The cause of the horrific explosion a century ago was never clearly established. Just six months before the blast a German U-boat had sunk a South Arklow light vessel and at the inquest into the deaths at the factory the manager, a Mr Udal, said the whirring sound heard by some of the workers indicated an attack from the sea. It was also revealed that a few weeks before the blast some workers had been reprimanded for being in possession of matches. A verdict of unknown causes was returned.

The plant did not long survive the war. It fell victim to rationalisation which led eventually to the creation of the chemical conglomerate, ICI. The works were purchased by the Hammond Lane Foundry in Dublin and the machinery was reduced to scrap. A pleasant wooded walkway now runs around the site beside a wild duck reservation.