Sorry, I have to disagree with RuthieB.
The star means that he had graduated, passed his exams ect for third class in whatever branch he was in. If there was a star under the badge, then he would be second class.
So that means he could have been an Able Seaman or a Leading Hand (Killick). Without a hook on his left arm it is very difficult to say what rank he is.
I cannot see enough of the badge to have a clue what branch he was in, sorry.
Salty