Following the recapture of the northern beachheads of Buna, Gona and Sanananda, the Allies moved onto the offensive in New Guinea. The PIB took part in the advance to Salamaua in 1943, before fighting along the Markham, Ramu, and Sepik rivers during the Ramu Valley – Finisterre Range campaign, and on the Huon peninsula, assisting in the capture of Finschhafen and Sattelberg, and pursuing the Japanese as they retreated along the northern coastline towards Saidor in 1943–1944. The battalion was temporarily withdrawn from operations to reorganise in 1944, and together with several New Guinea Infantry Battalions (NGIBs) that were subsequently raised by the Australian Army, the PIB was formed into the Pacific Islands Regiment (PIR) in November 1944. In 1945, it was deployed to Bougainville where the battalion's companies were spread across the fronts from Bonis to Buin during the final months of the war. Such was their effectiveness that the Japanese referred to the PIB as "Green Shadows" due to their ability to fade into and appear from the jungle unexpectedly, with its soldiers becoming noted for their ferocity and tenacity. After the end of the war the battalion was used to guard Japanese prisoners of war, before being disbanded in August 1946. In 1951, the PIR was reformed, drawing its lineage from the PIB and NGIBs.