Allied strategists knew that the Japanese Navy had occupied Tulagi in May 1942 and had constructed a seaplane base near there. Concern grew when in early July 1942 the Japanese Navy began constructing a significant airfield near Lunga Point on nearby Guadalcanal island. These bases, when complete, would protect Japan's major base at Rabaul, threaten Allied supply and communication lines across the South Pacific to Australia and New Zealand, and establish a staging base for possible future offensives against the New Hebrides, Fiji, Samoa, and New Caledonia.