After the Confederate attack on Fort Sumter, Lincoln called for 75,000 men to join the Union Army.[18] Weaver enlisted in what became Company G of the 2nd Iowa Volunteer Infantry Regiment, and was elected the company's first lieutenant.[19] The 2nd Iowa, commanded by Colonel Samuel Ryan Curtis, a former Congressman, was ordered to Missouri in June 1861 to secure railroad lines in that border state.[20] Weaver's unit spent that summer in northern Missouri and did not see action.[21] In the meantime, Clara gave birth to the couple's second child and first son, named James Bellamy Weaver after his father and Bellamy Storer.[22]