There have been no known Gunner-class Servants yet.
Other qualifying heroesEdit
|True Name||Current Class||Notes|
|Billy the Kid||Archer|
 Fate/Apocrypha material - Encyclopedia: Double Summon [Skill], p.176 [T]
Double Summon [Skill]
Double Summon. The skill possessed by Assassin of Red, Semiramis. It is an underhanded skill that is only invoked when certain conditions are met during the summoning, like a “command input on the title screen”.
Of course, this kind of skill has some restrictions, with the three Knight classes (Saber, Archer and Lancer) and some of the extra classes (like Ruler, Shielder and Avenger) incapable of being applied to the Double Summon skill. In other words, only a combination of the Berserker, Caster, Assassin or Rider classes is possible. However, thought rare, a modern day extra class like Gunner can apparently be combined with another class through this skill.