Ther mortar is the weapon (ordinance), the rocket is the projectile with a rocket driver.
Accuracy counts in speech as well as in the military - ignorance means death.
A rocket is a SELF-PROPELLED unguided weapon -
rockets do fall under artillery commands, as do missiles (guided self propelled weapons). two different types of weapons.
Generally speaking though, artillery pieces PROPEL a round of explosive etc)
artillery pieces are catagorized by the angle of attack - different angles, different names ---
mortar - steepest angle up to 90 degrees (don't forget windage)
howitzer -
cannon -
rifle / gun - "flat" trajectory such as the Recoiless Rifle etc.
A rocket streaking across the bow of a ship does not appear to be a "mortar" - it would have been coming straight (or so) down. Rockets may be fired at ANY angle and be free-standing or fired from a launch platform that could even be a 'mortar tube' but that does not make the rocket a "mortar rocket"
I was just amused (not) by the inappropriate weapons designation from a supposed military dispatch.
"Picky-picky. Who cares?" ask the masses...
"The Deliberate Dumbing Down of America: A Chronological Paper Trail "
http://www.amazon.com/exec/obidos/ASIN/0596009410/ref=nosim/spadata-20