This is a silly question that is only spurred by my own ignorance and curiousity. Whats the difference between a missile and a torpedo? A torpedo, according to what I understand can be fired in or above the water. Is that the sole difference? Because a missile is obviously fired from above the water and I’m assuming can be fired under it.
But I don’t know, which is why I’m asking.
The simple answer:
Torpedoes travel through the water to their target.
Missiles travel through the air to their target.
That’s the simple answer. I’m sure someone will be by shortly to give a more substantial answer.
More substantial how? 
You can’t shoot down an F-15 with a torpedo for example?
Nope. Trident and Polaris, to name but two, are fired from (just) beneath the surface.
I wonder if looking at the end phase would be more instructive?
The meaning of the terms isn’t always that clear-cut. They also change over time.
Prior to ~1900 a “torpedo” was any explosive weapon other than artillery. That usage survives today in some military blasting devices used for destroying enemy defensive fortifications.
In 1950, a missile was an explosive weapon which traveled through the air or through space and which had guidance capability to track its target.
In 1950, a torpedo was an explosive weapon which traveled through the water and which had guidance capability to track its target.
And that’s pretty much the non-specialist definitions today. But there ar a lot of hybrid cases now which make it difficult to say exactly where one begins and the other ends.
By 1970 we had missiles launched from just below the water surface (as noted above), and missile/torpedo combinations which flew through the air for miles, then dove into the water & attacked their target in the fashion of a traditional torpedo.
By the 1980’s we’d invented the opposite, a device fired from a submerged submarine torpedo tube which went some distance underwater, broke the surface and flew through the air the remaining several hundred miles to the targetbefore attacking it in the fashion of a traditional missle.
Now we have missiles that are launched from below the water’s surface but which never get wet; they are pushed to the surface inside a gigantic bubble of gas. And there are torpedoos that travel the same way, generating a gaseous envelope around themsleves so they remain dry, or nearly so, depsite being launched underwater, traveling miles underwater and impacting their target underwater.
I think the main difference is the manner of their propulsion. Missiles generally travel by rockets. Torpedos generally travel by propellors. But there are some exceptions. Some of the early missiles were fitted with propellors and some modern torpedos are fitted with rockets.
A torpedo does not even have to be propelled, nor it is an underwater weapon either.
Torpedos originally were demolition tools, and explosive charge on the end ot a long pole, someone got clever and realised that the shape of the charge was critical, and shaped it.
This allowed the charge to penetrate metal and wood.
The earliest underwater weapons were made in this form, they were just charges on the end of a pole, IIRC they had an awl on the end, and were literally screwed into a target ship.
Another type of torpedo was famous during the D-Day landings, this was used to destroy a barricade and allow the Omaha beach landing to advance.
This again was an explosive charge, on the end of a pole, it was actualy a series of poles that screwed together end to end, thus extending the reach.
The usual use of the word is associated with maritime use, or on Star Trek if you happen to be that way inclined, but it also has a much older use.
…and while I’m at it, read this,
http://www.cmonitor.com/apps/pbcs.dll/article?AID=/20071011/STATICPAGES0209/710110301/1043/NEWS01
By way of historical reference, Admiral David Farragut’s famous “Damn the torpedoes!” quote at the US Civil War Battle of Mobile Bay was in reference to moored naval mines, which were then known as torpedoes, not the self-propelled ordinance we know as torpedoes today.
Torpedoes are damned; missiles are towed.
Do you mean the gaseous envelope stays around the torpedo for miles? That’s a bit counterintuitive to me – can you help with a link?
If that’s the same device that I saw used in a movie about D-Day, wasn’t each segment filled with explosive? It looked like it was designed to clear a path through barbed wire, mines, and other obstructions. Sort of like the rocket-propelled line charges used in the first Gulf War.
The first “cruise missile” (if it could be called that) was the Sperry Aerial Torpedo
I don´t know at what point such things started being called missiles though.
I love the Dope…