Mission is a perfectly valid word for describing an outing of a submarine, specially when most of the discussion is surrounding the technical aspects of it. Do you also get angry when a business describes something as mission critical?

> Do you also get angry when a business describes something as mission critical?

Not if they are doing something useful to others.

Are hikers who get lost on a mission?

mission [1]:

    (1) a specific task with which a person or a group is charged
    (2) a definite military, *naval*, or aerospace task

So in answer to your question, yes. If hikers wanted to call their hike a mission it is well within their rights. Merriam-Webster isn’t going to stop them.

You should seriously find better things to do with your life than obtuse rebellion against dictionary definitions. It makes you look like an illiterate nonce.

[1] https://www.merriam-webster.com/dictionary/mission

You're the one who cited the dictionary.

You complained about diction. I cited a dictionary.

It's actually really common in the outdoor recreation world to refer to an outing of some sort as a mission.

I refer to a trip to the grocery store as a mission sometimes

Yes, this is not an uncommon usage of the word.

Sadly puffery and euphemism are all too common.