 The Japanese Twenty-Eighth Army under Lieutenant General Shōzō Sakurai, after retreating from Arakan and the Irrawaddy valley, had reached the Pegu Yomas, a range of low mountains, hills and uplands between the Irrawaddy and the Sittang River in central Burma.They were joined by Major General Hideji Matsui's 105th Independent Mixed Brigade, also known as "Kani" Force (men of anti-aircraft batteries, airfield construction battalions, naval anchorage units and NCO schools) which had faced IV Corps.The Japanese trapped in the Pegu Yomas prepared a break-out operation to rejoin the Burma Area Army and escape into Thailand with them.