Well wiki say that: Dreadnought cut the submarine in two after a short chase. So I think they want to ram it.
Oh,
Dreadnought did
intend to ram the sub.
The fact is that she wasn't
actively hunting the submarine; the sub lost depth control after not compensating for a torpedo launch.
Dreadnought was simply looking the right direction at the right time, and the sub magically appeared just off her bow. An
accident caused by a diving officer's mistake caused the sub to broach, and
Dreadnought took advantage of her high speed to catch the sub and ram her.