The government's decision to remain neutral limited the impact of the second world war on Ireland. Many UCD students enlisted in the armed forces, while UCD scientists and engineers served on the Emergency Scientific Research Bureau, which advised the government on how best to overcome shortages of fuel, raw materials and equipment. During the war years the laboratories in Merrion Street were used for research into the chemotherapy of tuberculosis, typhoid carriers and the production of penicillin, alongside other studies on the viability of substitutes for materials no longer easily available. Other research activities continued throughout the decade, and the Boyle Medal, the highest research honour of the Royal Dublin Society, was awarded in 1942 to Joseph Doyle, professor of botany, and in 1945 to Thomas J. Nolan, professor of chemistry. Another prominent professor in Merrion Street during this period was professor of zoology James Bayley Butler, whose inventions included processes for canning peas, for treating dry rot and for waterproofing maps, the latter the subject of a patent which he sold to the U.S. Army during the war.

The number of students in UCD increased steadily during the war and post-war years, and government funding increased from £82,000 to £124,542 in 1948 to support this expansion. This allowed some improvements in the teaching and research facilities in the college, including the provision of new laboratories in Merrion Street, but UCD was now the largest university in Ireland and the question of accommodation became a serious subject for discussion. The possibility of building on lands adjacent to Earlsfort Terrace was explored, but it was concluded that increasing student numbers would render a city-centre site an unwise investment, and attention focused on the lands in Stillorgan around Belfield House.

Ireland in the post-war years offered new opportunities to science and engineering graduates. The Industrial Development Authority was established in 1949 to encourage industrial development, there were new construction projects, Bord na Móna was expanding its operations and in 1946 the ESB commenced its rural electrification scheme, which was to transform all aspects of Irish rural life over the next decade.

Above: Civil Engineering students, 1943