In this task, you're given a passage, further information available on a particular linked term from the statement, and a question. Your job is to generate the answer to the question by using the information provided. If there is no clear answer obtainable, output 'none'.

Passage: In 1934, the 12th took part when the Army was given responsibility for flying the mail after President Franklin Roosevelt cancelled all civilian contracts because of alleged rate-fixing by the airlines. 12th pilots were assigned to the difficult and dangerous CAA Route 18, from Salt Lake City, Utah to Oakland, California, via Elko, Nevada, and Sacramento, California. The aircraft they flew were primarily Douglas Y1B-7 bombers. On 1 June 1937, the 12th Observation Squadron left Texas to operate with the 7th Cavalry Brigade, the mechanized forerunner of the First Armored Division, at Fort Knox, Kentucky. While stationed at Fort Knox, the squadron participated in field maneuvers with the mechanized cavalry near Fort Oglethorpe, Georgia, and at Fort Riley, Kansas, in 1938; in the First Army maneuvers at Plattsburg, New York in 1939; and in the Third Army maneuvers in Louisiana in 1940. In the summer of 1940, the squadron was the first to be attached to an armored division the First and on 2 December, a base detachment was formed at For. Knox to manage Goodman Field, a new and modern airfield still under construction. Captain Robert M. Lee, commanding officer of the 12th, was also detachment commander. Along with the First Armored Division, the 12th Squadron played an active role in the Carolina and Louisiana Maneuvers from July to December 1941. After those maneuvers, the 12th returned to the recently completed Godman Field, where the unit supplied a cadre to organize the Headquarters Squadron of the 73d Observation Group.
Link Information: .

The depository was built by the Treasury in 1936 on land transferred to it from Fort Knox. Question: Of the forts that participated in field maneuvers in 1937, which was the oldest?
Answer: Fort Riley