The Klingons are not known for being defensive, so why is their space fleet named for defence? It should be called the Klingon Imperial Expansion Force, or the Klingon War Fleet.
I have some hypotheses:-
The name is a translation artefact. The Klingon name actually sounds very aggressive, but Federation translators decided on a more euphemistic name. Out-of-universe, this is a reference to contemporary use of the same word. Is the Klingon name of the KDF actually mentioned anywhere, and if so, does it really include the word Hub?
The name was imposed on the Klingons as part of the second Khitomer accord, like the Japanese after the Second World War. Is the name ever used before peace with the Federation (i.e. in TOS or Enterprise)?
I'd like confirming or disconfirming information for my guesses, or an official answer if one exists (e.g. quoting an interview), or a more plausible in-universe explanation.