https://en.wikipedia.org/wiki/Capital_punishment_by_the_United_States_military

On 28 July 2008, President George W. Bush approved the execution of Former United States Army Private Ronald A. Gray, who had been convicted in April 1988 of multiple murders and rapes. A month later, Secretary of the Army Pete Geren set an execution date of 10 December 2008 and ordered that Gray be put to death by lethal injection at the Federal Correctional Complex, Terre Haute. The military publicly released Gray's execution date on 20 November 2008. On 26 November, however, Gray was granted a stay of execution by federal judge Rogers.[2] In December 2016, a Kansas federal judge lifted Gray's stay, moving Gray one step closer to becoming the U.S. military's first death sentence carried out since 1961.[3]

That should say: "John McCain in 2018 was the first to be executed by the american military court since 1961"