U.S. District Court Judge Walter Smith also ordered Oscar Alonzo Acosta to remain under supervised released, and to pay a $1000 fine.
Acosta will be imprisoned in the federal prison in the Bryan/College Station Area.
A federal complaint filed by FBI agents who investigated the allegations says Fort Hood Military Police discovered the encounter on February 14th in the recreational area. The MPs were following up on a criminal trespass incident.
As the MPs approached the vehicle they saw Acosta engaged in sexual relations with the girl, who was 14-years old at the time. Acosta is 26.