Original: The growth of the ministry in the 1940s and 1950s made this increasingly impractical, and in 1956 Robert Menzies created a two-tier ministry, with only senior ministers holding Cabinet rank, also known within parliament as the front bench.
Simplified: With more ministers added in the 1940s and 1950s this made the cabinet too big. In 1956 Robert Menzies created a two level ministry, with only senior ministers in the Cabinet.