The post-war growth of corporations was paralleled by a reduction in the number of Departments. Between 1946 and 1954 twelve Departments lost their separate identities, and the number of independent units declined from the wartime peak of 53 to 41. This was the most effective attempt that had been made to reorganise the work of the Public Service into a more compactly grouped departmental system. The rearrangement of functions was accompanied by adequate structural alterations within Departments. The enlarged units were reconstructed so that they worked as unified administrations instead of as loose federations of semi-autonomous units as had been the case with earlier amalgamations. A further change was made on 1 April 1962 when the Broadcasting Service became a public corporation. Yet the Service continues to be unwieldy and, in the absence of a more rational grouping of activities, coordination and control is achieved, in part, through the use of an extensive network of Cabinet committees, and inter-departmental committees and working parties.

In 1961 the Government appointed a fourth Royal Commission to report on the State Services. The Commission recommended that some organisational changes be made and that others be investigated further. As a consequence a separate Department of Civil Aviation was established, and a Ministry of Defence was set up to absorb the rest of the Air Department and the Army and Navy Departments. Other proposals are at present under examination.

The 39 Departments in existence at 31 March 1964 were: Agriculture, Audit (Office), Civil Aviation, Crown Law (Office), Customs, Defence, Education, Electricity, External Affairs, Forest (Service), Government Life Insurance (Office), Health, Industries and Commerce, Inland Revenue, Internal Affairs, Island Territories, Justice, Labour, Lands and Survey, Law Drafting Office, Legislative, Maori Affairs, Marine, Mines, Police, Post Office, Prime Minister's, Government Printing Office, State Advances Corporation, State Services Commission, Public Trust (Office), Railways, Scientific and Industrial Research, Social Security, State Fire Insurance (Office), Statistics, Tourist and Publicity, Transport, Treasury, Valuation, and (Ministry of) Works.