What I am talking about is the Spartan Secret Police (cannot remember the name at the moment). Their job was to keep the Helots and subject polis in line by assassinating any leaders with anti-Spartan tendencies. They were trained to a level that made even the Spartiatai look un-bad***.
In times of great crisis, such as the battle of Thermopylae, they could be employed to assassinate enemy commanders and sabotage their supplies and weapons. They nearly succeeded in assassinating Xerxes on the third day of the battle of Thermopylae (which I've read (the book Thermopylae, battle for the West) lasted about a week. This is also supported by the History Channel, saying that Xerxes was held up for two weeks (which makes sense if you take into consideration that he ordered 3/4 of his dead soldiers buried so that the sailors could be shown the battleground without losing too much morale).
They are, to my knowledge, the most obscure and unknown about branch of the "Spartan Military" (in their case it does necessitate the comas), and those are the only concrete mentions of them I've read.
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