The potential for some kind of action was considered seriously by both US and Canadian Forces. When the US was finally drawn into World War II, the defense of Alaska had already been underway - but no one knew the where, when or how the Japanese would attack. It came in a stunning surprise attack on Dutch Harbor 3–5 June 1942; farther west, Imperial Japanese forces seized the islands Kiska and Attu, bringing ashore some 7,000 troops (at Kiska) and nearly 3,000 at Attu.