An 1862 law allowed honorably discharged Army veterans of any war to petition for naturalization, without having filed a declaration of intent, after only 1 year of residence in the United States.
Variations of this special treatment continued throughout the years.
The wording of the 1862 Act stated that any alien, age 21 or up "...who has enlisted, or may enlist in the armies of the United States...."
It was designed to encourage enlistment during the Civil War. Aliens serving in the US military did not gain citizenship through service alone.
The naturalization of soldiers was performed under certain provisions of nationality law facilitating the naturalization of members of the US armed forces. These
provisions waived the Declaration of Intention requirement and waived or reduced the residency requirement. Many soldiers filed petitions and were naturalized the same day.
See SPECIAL CASES: Military for more details
Instead of naturalization "first papers", some courts filed military discharges. Sometimes you will have to consult separate military indexes but you should start looking in the usual places first. Military naturalizations were included in the WPA Project indexes (You can read about the WPA Project and naturalization indexes, and view an online one for all of Arkansas for 1809-1906
If the naturalization took place in a Federal court, naturalization indexes, declarations of intent, and petitions will usually be in the NARA regional facility serving the State in which the Federal court is located. Some of these indexes and records have been microfilmed.
Naturalization records from county courts may be at the county court, in a county or State archives, or at a regional archives serving several counties within a State.
Some county court naturalization records have been donated to the National Archives and are available as National Archives microfilm publications. These are listed under the state in which they occurred, at NaturalizationRecords.com
Scroll down to the state list at the bottom of the page.