The regiment was mobilized at Ft. Riley in June 1916 and sent to Eagle Pass, Texas. They served there for about four months. Their time was characterized by monotonously watching river crossings—there were quite a few on the Rio Grande in the low-water season—and by training exercises. There was no combat, not even a desultory pot shot or two. 

Naismith took his calling as the chaplain very seriously, approaching the task just like coaching a team of his young players, encouraging them to realize their potential. He conducted church services, counseled soldiers, and advised his CO as to the spiritual needs of the unit. He was particularly concerned with efforts to keep the troops away from prostitutes, gambling, alcohol, and brawls with the locals. To this end, and to keep them busy and physically fit, he organized basketball games, baseball games, and boxing matches involving the entire garrison at Eagle Pass. 

Back in Lawrence, when war was declared, Naismith sought to have his inactive National Guard chaplaincy transferred to active duty status, but he was turned down flat: he was a Canadian citizen and he was way too old. 

But he found another avenue of service that was open to him. As the ranks quickly swelled, the Army was woefully short of chaplains and concluded agreements with service organizations to provide spiritual guidance and support if not actual religious celebrations. One of these was Naismith’s old friend the YMCA.