Corporal
From Tardis Wiki, the free Doctor Who reference
Corporal was a military rank for some Earth-based militaries or armed forces. The rank of corporal was above that of Private. (PROSE: Freedom) Being low down the military rank structure they were often relatively young compared to other personnel. (PROSE: Illegal Alien, The Dying Days)
Corporals, like other military personnel were identified by their uniform; (PROSE: Independence Day) stripes in a corporal's case. (PROSE: Vanderdeken's Children)
Within some Earth-based militaries other terms were used such as obergerfrieter. (PROSE: Casualties of War)
When he first met the Doctor, John Benton was a Corporal. (TV: The Invasion)