 The majority of the airfields were between Rangoon and the Axis advance and as the Japanese gained use of the airfields in Tenasserim, the amount of warning the Rangoon airfields could get of attack decreased, and they became more and more untenable.On 22 January 1942, the main body of the Japanese 55th Division began the main attack westward from Rahaeng in Thailand across the Kawkareik Pass.The 16th Indian Infantry Brigade of the 17th Indian Division guarding this approach retreated hastily westward.