Historically midshipmen would be young lads of 12 or 13, and therefore couldn't have a full sized weapon - as such, they were given a small sword, known as a Midshipmans Dirk until they grew old enough to carry a larger weapon.
Not to be confused with the Scottish Dirk, which is smaller - it's a different weapon basically.
Anyone wearing it with No2's would be quite rightly ripped to shreds. Very throbberish IMHO Plus it counts as a sword, so whoever it was wouldn't have been able to hang it on the swordbelt, so would have had to carry it all night - poor drills!
And no, I don't even think the Naval Pattern is recognised anymore, Middies parade with a full sword so there is no need to have the shorty version.
haha, no, I've only ever seen one for sale and had never seen one before, and wikipedia gave me no help Besides, its not on the kit list Wouldn't you rather discuss swords then whether your blazer is correct because it has 2 buttons etc!? (mine does have 2 buttons btw)