Following their defeat during the Battle of the Coral Sea in early May the Japanese invasion fleet bound for Port Moresby had been forced to turn back, while on 4 June the Japanese were decisively beaten at Midway by the US Navy. Despite these setbacks though Japanese forces in Rabaul and Lae appeared to be preparing an attack against Port Moresby from northern Papua, via Buna and Kokoda. During this time the only Allied unit in the South West Pacific Area still actively engaging the Japanese was Kanga Force, made up of the NGVR and the 1st and &lt;a href="2/5th%20Commando%20Squadron%20%28Australia%29"&gt;2/5th Independent Companies&lt;/a&gt;, fighting a guerrilla campaign against the Japanese around Lae and Salamaua. In June 1942 Morris tasked the PIB with reconnoitring the Awala–Tufi–Ioma area. To meet the Japanese threat the Allies planned to construct airstrips in the Buna–Dobodura area to facilitate operations against Rabaul and to secure it in order to forestall any advance from that direction. As the situation worsened, the PIB—with a strength of just 30 officers and 280 men—was sent forward to patrol the northern coast of Papua and was subsequently dispersed over a wide area. Along with the 39th Battalion (less one company), and supply and medical detachments, they formed part Maroubra Force.