Subarmalis or gambeson?

[Atawulf]

The photo doesn't tell us whether it is meant to wear under armour or whether it is meant to be worn by itself.

This gambeson of picture is to wear under the armour, in my case would be under chainmail.
Looking the DRB pictures I think a thoracomacus with long sleeves wolud be appropiate. I know the pictures are later of the original but I think the description was the same, a thoracomacus like a tunic.