The Japanese attack on Pearl Harbor on December 7, 1941 plunged the United States into World War II, a war that historians say killed more people, cost more money, damaged more property and brought on more far-reaching changes than any war before or since. Factories were converted to war-time production and more women began working in manufacturing plants as men went to war. Many products were rationed as fair distribution and price controls were instituted to combat inflation.

The Monaca, Pennsylvania plant was purchased from Pittsburgh Hanger Company on Pearl Harbor Day and F. N. Barnes who had worked for Pittsburgh Hanger was hired to manage that operation. He later became a member of the Board of Directors and served in that capacity until his retirement.

Laidlaw was not converted to the manufacture of war supplies, but was fortunate to receive a priority rating from the war department to set up the production of bale ties and some screen door springs. Bale ties were in great demand for the war effort. The Monaca and Peoria plants produced 1750 tons of bale ties monthly as the bale tie proved to be Laidlaw's lifeline during the war years. The manufacture of coat hangers ceased completely since all steel was reserved for the total war effort.

The wire handled flyswatter was replaced by one with a wooden handle and treated paper blade.

Laidlaw purchased Memphis Hanger Company in 1944 and moved it, and the Pittsburgh Hanger Company, to Monaca, Pennsylvania.