Block 2, a newly constructed building of three floors was occupied in 1939, main feature of which was the occupancy of the whole ground floor by the Forecasting Section.

On the outbreak of the Second World War in 1939, the Bureau (which by then was known popularly as the Meteorological Branch) was re-organised to meet essential war time commitments. A Training Section was formed, training of Forecasters and Observers was accelerated and in April 1941, a large staff was, enlisted as the R.A.A.F. Directorate of Meteorology. Mr. W. S. Watt, Commonwealth Meteorologist retired in January, 1941 and his place was taken by Mr. Warren, who from 1941 to 1946 was Group Captain and Director of R.A.A.F. Meteorological Services. For these years the control of the Meteorological Branch passed from the Department of the Interior to the Department of Air.

During the war years the service usually supplied to the civil population was carried on, but on a reduced scale, dictated by the exigencies of war, while a meteorological service was provided to the armed forces throughout the South West Pacific area.

In 1942 a temporary structure known as Block 3 was built. It housed the store on the ground floor with offices on the first floor.

After the war reversion to civilian status and to the Department of the Interior took place, and plans were laid for a re-organised service to meet the needs of the public which had increased greatly over those war years. The staff proposed in 1947 numbered 636, distributed as follows:— Central Office 96, Divisional Offices—Melbourne 20, Sydney 29, Brisbane 29, Adelaide 13, Perth 23, Hobart 13, and Field Staff 413. The 1946/47 vote for sal1aries was £214,300 and for Expenses £193,800, but contributions by the Department of Civil Aviation and Air reduced these to £44,300 and £78,700 respectively.

Bureau of Meteorology