When the United States declared war against Spain in April 1898, National Guard units from all over the country were called into federal service to complement the regular military. The state of Wisconsin contributed four infantry regiments and one battery of light artillery, almost 3,000 men, to the war effort.
Mobilization in Wisconsin took place the last week in April at Camp Harvey in Milwaukee. The soldiers of the first three regiments were mustered into federal service in the beginning of May, with the 2nd and 3rd Wisconsin Infantry Regiments receiving orders to go to Camp Thomas in Tennessee in mid-May. The 1st Infantry Regiment was ordered to Jacksonville, Florida later days later. At their respective locations, these three units spent time drilling and also began suffering from tropical diseases like typhoid fever and malaria. The 4th Infantry Regiment, not mobilized until the end of July, spent the summer at Camp Douglas, Wisconsin preparing for service.
Toward the end of July, the 2nd and 3rd Infantry Regiments were shipped to San Juan, Puerto Rico, and from there went to the city of Ponce where they disembarked. These units saw light action as they marched around the island, chasing the Spanish army. Hostilities ceased in mid-August, but the men of the 2nd and 3rd Infantry Regiments continued to take casualties as tropical diseases took their toll. The Second was sent home in late August and arrived in Milwaukee on September 9. The Third remained in Puerto Rico for mop-up duty, fighting a small skirmish at Aibonita Pass before returning to Wisconsin on October 24.
The 1st Infantry Regiment, which had remained in Jacksonville, also continued to suffer disease-related casualties. After Spain surrendered, the unit was sent home and arrived in Milwaukee on September 10. The 4th Infantry Regiment and the light artillery battery, which had not left Camp Douglas before the war ended, experienced almost no health problems. The battery was relieved from federal service on September 7, and one week later the men of the Fourth were sent to Anniston, Alabama from where it was thought they would go on to Cuba for garrison duty. Instead, they remained at their camp before being mustered out at the end of February 1899.
According to the state records, about 134 Wisconsin men died during the war in the Caribbean. Of those, 132 died of diseases and other health problems. Malaria, typhoid fever, and spinal meningitis were three of the most prevalent causes of the deaths. Only Corporal Oscar R. Swanson and Private Fred Vought, both of Company L, 3rd Infantry Regiment, died as a result of military action. Both were killed during the engagement at Aibonita Pass on August 28, 1898.
