The IRA created a massive propane tank cannon to fight the British
For almost 40 years, the Irish people endured a constant state of fear stemming from a low-level war that killed thousands of Irish civilians, British troops, and Irish fighters – all in a stunningly understated conflict called "The Troubles." While British and U.K. loyalist forces were well-equipped and armed for the task, the Irish Republican Army, fighting for a united Ireland, had to improvise a little.
This is why "Irish Car Bombs" are a thing.
The Irish Republican Army was a homegrown paramilitary organization that was at best outlawed, and at worst, designated a terrorist organization. They were committed to a fully united Ireland by any means necessary and resisted the United Kingdom's occupation of Northern Ireland, also by any means necessary. This usually meant improvised guns, bombs, and even mortars. That's how they created what British troops called the Mark 15. The IRA called it the "Barrack Buster."
Barrack Busters first started to appear in the IRA arsenal in the 1990s and was an improvised 36-centimeter mortar capable of firing three-foot-long propane tanks filled with high explosives. The Mark 15 was usually made of a cooking gas container created for use in rural areas of Ireland. It was capable of launching one of these powerful explosive containers nearly a thousand feet.
The IRA improvised mortars of various sizes and power, and hit not only military barracks, but bases and even 10 Downing Street.
The Mark 15 was described as having the effect of a flying car bomb, that has taken down barracks, helicopters, and even Royal Air Force planes. It was the fifteenth in a line of development that stretched as far back as the early 1970s. It was the largest homemade mortar developed by the Irish Republican Army. The development does stretch to a Mark-16, but that weapon was more of a recoilless rifle than it was a traditional mortar.
Introduction of the giant mortar did have an impact on British forces. The United Kingdom was forced to pull its checkpoints away from the Irish border after the introduction of the Mark 15 mortar. It was so effective as a weapon it was adapted for use by paramilitary forces in other countries and conflicts, including the FARC in Colombia and the Free Syrian Army in Syria.