The Kansas record might be for a Kansas National Guard enlistment. Do an internet search WWII Army and Army Air Corps Bases to see if there is a map. Contact the Arizona Historical Group. Was your mother living in Arizona in 1942? Seems to me Forrest would be stationed at a nearby base.
I find a Missouri Marriage License issued in Jackson County on May 1st 1943 to a Forrest H. Gardner of Hutchinson, Reno Co. KS and an Edith C. Green of Herrington, Reno Co KS. He is age 23 (b. 1920) and she is "over 21" and both single and free to marry. Then in a November 28th 1946 Reno newspaper list (divorce) degrees and one was granted to an an Ethel Gardner from Forrest Gardner.
1930 census for Kansas, Reno County Hutchinson Twsp is a Forest Gardner age 10 born in Missouri, parents are Oscar age 38 b. MO andRosa age 30 b. MO with siblings, older sister Clara age 12 b. MO, younger brother Herbert or Hubert age 6 b. MO and younger sister Johana4 yrs 11 mos born in KS.