Complex sentence: Although Frank Forde was Curtin's deputy, Chifley became the minister Curtin most relied on, and he controlled most domestic policy while Curtin was preoccupied with the war effort.
Split into simpler sentences: Although Frank Forde was nominally the number-two man in the government, Chifley became the minister Curtin most relied on. He controlled most domestic policy while Curtin was preoccupied with the war effort.