Penang's residents also had to endure economic hardship during the Japanese occupation, with hyperinflation caused by the oversupply of the Japanese-issued 'banana' dollars, and the acute shortage of food and raw materials, due to a combination of Japanese wartime rationing and an Allied blockade of Japanese shipping. Households were forced to turn to secondary crops such as sweet potatoes, yam and tapioca for their own subsistence. Beginning in 1942, a standardised Japanese curricula was enforced in all schools throughout Penang, with Japanese as the official language. In fact, social lifestyles were also greatly impacted, as it became compulsory to bow to Japanese soldiers on guard duty and to sing the Japanese national anthem, whilst whole streets and shops were renamed in Japanese.