Like the Allies, the Japanese also relied on water transport to ferry supplies and reinforcements around the New Guinea, using a force of three submarines to avoid interdiction by Allied aircraft which had previously inflicted heavy casualties during the Battle of the Bismarck Sea. These submarines were augmented by barges, although they were limited in supply and were subject to attack by Allied aircraft and PT boats. Once the supplies had been landed, resupply parties were used to carry the stores overland on foot along a number of key tracks to their main troop concentrations around Sattelberg and Finschhafen. Air support was provided by the 4th Air Army, consisting primarily of the 7th Air Division and 14th Air Brigade, along with some elements from the 6th Air Division. Based in Wewak, the Japanese aircraft were mainly used to escort Japanese shipping and attack Allied shipping around the main beachhead during the campaign, with a secondary task of undertaking ground attack missions in support of Japanese troops. The 11th Naval Air Fleet, based at Rabaul, also undertook anti-shipping missions. Despite having these units available, heavy Allied bombing of Japanese airfields around Wewak in August 1943 greatly reduced the number of aircraft available to the Japanese and limited their ability to apply airpower throughout the campaign.