Maeda became the Japanese naval attaché to the Netherlands in 1940. Following the German invasion of Denmark and Norway, he warned the Dutch that an invasion of their country was certain and they began to prepare accordingly. In October that year, he went to Batavia in a diplomatic mission attempting to secure trade between the Dutch East Indies and Japan – particularly in oil. In addition to trade negotiations, he was also tasked with espionage and establishing a fifth column, supported by civilians such as Shigetada Nishijima. Maeda returned to Japan in mid-1941, when he was made deputy of the European Affairs section under his elder brother Minoru Maeda.