In 1991, barrel bombs were used by Croatian forces against Serbian forces during the Battle of Vukovar, where they were dropped from Antonov An-2 agricultural airplanes. The device was called the "Bojler Bomba" ("boiler bomb") as it was made by filling ordinary household hot water boilers with explosives and shrapnel. The effects were predominantly psychological. As background, a Croatian airforce was established in 1990, made up of volunteers from a sports club at Sinj. They were private individuals and enthusiasts. Their weapons were home-made and improvised. "Bojler Bomba" are now on display at a number of museums in Croatia including the Technical Museum Zagreb and the Military Museum of the Croatian Ministry of Defence. Human Rights Watch (HRW) also reported a first-hand account of a boiler bomb being used in ground combat in Zlatište. A boiler bomb was rolled down a hill into enemy trenches while snipers tried to blow it up before it reached their position - it eventually got stuck in a tree and "all it did was destroy a lot of trees".