Mk 23 Torpedo?

[Zero Niner]

So I was fooling around with SH4 career mode & started a new career with a Gato class in Brisbane; I picked 1943 as the starting year and the game had me start in March.
In the torp screen I noticed Mk 23 torpedoes. I'm not too familiar with this, and tha game doesn't give an explanation, so could somebody briefly describe this particular type of fish?

Thanks.