The 1973 oil crisis started in October when the members of OAPEC proclaimed an oil embargo. That year, Egypt and Syria launched a surprise attack on Israel on the holiest day of the Jewish calendar, Yom Kippur. As Israel was vastly outnumbered, it went on full nuclear alert, loading warheads into planes and long-range missiles. Based on this, the United States chose to re-supply Israel with arms and in response, OAPEC decided to "punish" the United States. It lasted until March 1974.