It's perfectly plausible for a torpedo to penetrate the steel hull of a ship by just kinetic energy.

We (ie RNoN) "inheritated" over 1200 ex-german G7a(TI) torpedoes after the war, which went into our arsenal (it was actually kept in service - with several modifications - until 1999).
We had at least one well-known incident from the 70's (or early 80's) when an exercise torpedo malfunctioned and physically hit the targetvessel (an Oslo-class frigate), penetrating and lodging itself in the hull.