Why does this script work correctly?

Hello,

Here is the script I did after some testing, but I don't get why it works.

function FixedUpdate() {

    transform.Rotate(Vector3.up  * Input.GetAxis("Horizontal"));

    if(Input.GetAxis("Vertical") > 0)
    {
    transform.Translate(Vector3.forward * ( Input.GetAxis("Vertical")));
    //rigidbody.AddRelativeForce(Vector3.forward * (1000000 * Input.GetAxis("Vertical")));
    }
}

I have a game object which implement a rigid body component and the script above, and which contains my ship's object (mesh + collider etc).

The script works the same way with the commented part instead of the line right above.

My question is : why my translation works correctly since I never transform the direction it follows according to my rotation?

I mean, I usually did(or saw) things like

myDirection = transform.TransformDirection(myDirection);

to take care of the rotation, but this script works perfectly without that.

Can someone explain me why?

Thanks.

ps : I'm new to unity, so please don't be rude ;)

If you take a look at the scripting reference on Transform.Translate you will find out that the given vector is treated as local direction by default (relativeTo = Space.Self). That's why your direction refers to the local forward (z-axis)