The Rhodesians' means to continue the war were also eroding fast. In December 1978, a ZANLA unit penetrated the outskirts of Salisbury and fired a volley of rockets and incendiary device rounds into the main oil storage depot – the most heavily defended economic asset in the country. The storage tanks burned for five days, giving off a column of smoke that could be seen 80 miles away. Half a million barrels of petroleum product (comprising Rhodesia's strategic oil reserve) were lost. At a stroke, the country's annual budget deficit was increased by 20%.