An atheist chaplain is of course a contradiction in terms, an oxymoron.
Chaplain is Old French chapelain from medieval Latin capellanus 'custodian of the cloak' (of Saint Martin).
A chaplain is a member of the clergy attached to a chapel, specifically one officiating in the private chapel of a household or institution, on board ship, or for a Regiment, school etc.
The term also applies to a nun who recites the inferior services in the chapel of a nunnery.
Just sayin'..........