("Defense")
The security force of the Yishuv was established in Palestine in 1920 as a clandestine defense organization for the purpose of protecting Jewish life and property against Arab attacks. In 1941, it created a commando or "striking" force, the Palmah (a full-time military force of volunteers, something of a professional and elite unit), which later provided a large proportion of the senior officers in the early years of the Israel Defense Forces (IDF). Officially, Hagana ceased to exist on 31 May 1948, when the IDF was constituted.
Historical Dictionary of Israel. Bernard Reich David H. Goldberg. Edited by Jon Woronoff..