Admiral Holdo's tactic in "Star Wars: The Last Jedi" - Why is this not used more?

First, let's make 2 assumptions:

• Hyperspace collisions have happened in the past. In general, people know the consequences, and they know it's very messy. ("Ain't like dusting crops, boy!")

• The rebel military leaders aren't stupid. Admiral Akbar, General Organa, and Vice-Admiral Hondo fully understand what a "Hyperspace Kamikaze" attack would accomplish, and they've simply chosen not to do it until now.

Now, speculation on why we haven't seen it before:

1. Relative ship size matters. If an X-Wing tried to hyperspace through the Death Star, nothing would happen except the X-Wing blowing up.

2. The smaller ship gets disintegrated. There's a serious cost/benefit analysis, and only in a "last resort" situation (like we saw in this movie) does it actually make sense to sacrifice such a big ship in a suicide attack. The ship being "suicided" would need some serious size and shields to get close enough before being destroyed - and then it's gone forever. The First Order probably has enough resources to waste ships, but the Rebels definitely don't.

3. It's been done before, and the Empire already knows how to thwart it. General Hux is warned well before the collision that The Raddus is "preparing to go to hyperspace". In his hubris, he ignores the warning, saying "It's empty. They're just trying to draw us off". As soon as General Hux realizes what's happening, they start firing on the ship - it's just too late. If he had been less cocky, he might have heeded his minion's warning and destroyed it (or at least disabled it) before the disaster.

This question opens up a giant can of worms and potentially changes the entire paradigm of ship-to-ship combat in the Star Wars universe.

First issue: hyperspace is supposed to be an alternate dimension. Even in the 70's, we knew that accelerating an object to the speed of light isn't actually possible (I think). Except now, it look like hyperspace might be achieved by actually accelerating the ship to light speed. Makes for some serious weirdness.

Second issue: Admiral Holdo may have just invented the greatest anti-capital ship weapon of all time. Like, you said, you could strap hyperdrive's onto rocks and suddenly you've got massive ship killers. Or (and this is a question that's always bothered me about star wars) you could build a missile, maybe about half the size of an A-wing fighter with a hyperdrive in it (I think A wings have hyperdrives in one of the movies) and just program them to seek and destroy enemy ships. If it was moving at the speed of light, it would obliterate pretty much anything it came in contact with (In fact, if Holdo's ship was moving at light speed, the incredible part is that snokes entire ship wasn't obliterated (relevant xkcd). This would be THE new weapon. At the range where Holdo launched her assault, the laser batteries (and calling them lasers does hurt me a little bit) on Snoke's flagship weren't powerful enough to penetrate her cruiser's shields. If she had a battery of these missles should could simply have launched them from standoff range. The missiles could be shot down while deploying (launching a missile into hyperspace while it's still on your ship just doesn't sound smart), but the most powerful weapons on what is probably the most powerful ship in the most powerful military force in the galaxy would actually be powerless to do anything else. And considering how bad laser batteries in star wars are at shooting down fighters, I wouldn't be too worried about point defense.

Some potential issues (and solutions!) with this hyperspace missile:

If hyperspace isn't actually light speed travel, but massive acceleration is merely part of the process of reaching light speed, then were would be a relatively small window in which the the missile could impact before being in a different dimension. Let's assume this is true, because otherwise starship combat becomes suicidal.

This makes the missile slightly less unstoppable, but there's no reason that the missile couldn't evade (you know, like...droid starfighters). Or maybe you launch missiles in saturation waves, or you have dedicated bombers that carry these hyperspace missiles (because seriously, why the hell do SPACE BOMBERS have GRAVITY BOMBS).

Presumably, the creation of such a weapon would result in some better point defense (point defense in Star Wars is pretty pathetic). Assuming that the missile have to move at starfighter speed to "detonation" range, i.e. launching into hyperspace, defense would probably take the form of escort fighters (which already exist) and missiles launched from starships (and why the hell do missiles only come from fighters in star wars. Nobody thought to make a giant missile and put it on a capital ship? WHERE ARE MY PHOTON TORPEDOES.)

Main point? The age of starship battles is dead. Just like in the real world. We'd have escort ships and starfighter carriers because missiles defended by fighters would be more deadly than mysterious energy packet launching guns (seriously, I think the "lasers" that Snoke's flagship was carrying had projectile drop. LASERS. WITH PROJECTILE DROP. IN MICROGRAVITY), and the best defense against them would be fighters screening the capital ships outside of "detonation" range.

So Star Wars has some weirdness in it. Always has. Probably always will. I still had fun.

This was a different case - the rebellions were fleeing away in smaller ships with the assumption that they weren't been seen. Deathstar was mainly aiming at destroying the cruiser.

But when they came to know about the rebellions fleeing they changed their aim to destroying them without having any idea of anyone being present in the cruiser.

Now in a normal scenario of a war, taking such an action might not be fruitful in all the cases -

• Say the aim of the cruiser to be shot at lightspeed misses the target? It will eventually hit something somewhere.
• In the current case, General Hux or anyone on Deathstar was unaware of Holdo being on the cruiser, and the cruiser was not being shot at as well. This gave Holdo an opportunity to do so; otherwise, in a different case, it just might not be that practical.
• Holdo had nothing to loose here. She had a sole motive - to save the rebellions - and she had a big enough ship to use as a weapon. Considering the situation that had formed, she had the option of taking this action. But in a normal war, taking this step wouldn't be a sure-shot tactic, and something that a general would do.

What if the lightspeed rock missed the target? It would eventually hit something, which wouldn't be great. With Admiral Holdo still steering the cruiser, if it missed she could still take it out of lightspeed and avoid unintended damage to others.

Previously, a lightspeed rock could not be piloted remotely, since the ability to track an object at lightspeed is "new tech".

It was a WAR CRIME! Hux even refers to the resistance as "war criminals" early in TLJ, so clearly the concept exists. He is probably referring to the destruction of Star Killer base, conveniently ignoring his own mass genocide. But if not an explicit war crime, then using a ship as a kamikaze is probably an atrocity in the Star Wars universe, something that no one would seriously consider. Like chemical gas attacks, nuclear artillery, or other powerful but distained weapons we have today.

Hux clearly recognizes the possibility of Holdo's attack when he realizes that she has turned her ship towards the FO fleet and is preparing to jump to lightspeed since he immediately orders all vessels to fire on her cruiser even though he knows it is empty and not a direct threat. So this is something that is known to soldiers, but for some reason isn't a "go to" tactic.

On the technical front (to the extent that Star Wars movies obey internal consistency and science) I'm not sure Interdictors have made it into movie canon (these are Star Destroyer-like ships that use gravity generators to pull ships from hyperspace) but since they can stop ships from making the transition to hyperspace then it is also possible that normally a ship with an active anti-gravity system can stop another ship from hyperspacing through it, leading to just a normal collision like what we see at the end of Rogue One (Vaders Star Destroyer pops in on the rebel fleet, immediately crashing into some smaller ships trying to escape into hyperspace). This is discounted by the hyperspace jump in Rogue One, where they jump essentially from a planets surface, right through the atmosphere. Going through an atmosphere at high velocity is also extremely damaging, but presumably the U-wing shields protect it until it reaches space (though our physics would show that a few miles of atmo would be just as damaging as running into a solid object when travelling at a decent percentage of lightspeed).

Holdo was at the perfect distance to accelerate almost to the transition to hyperspace right at where Snokes massive ship was sitting, making a target that she couldn't miss. The collateral damage wrecking the rest of the fleet was just bonus. It was a 1 in a million chance and she took it.

Interestingly enough, if you examine all the other Star Wars cinematic battles there aren't really other opportunities to use this tactic. In ANH it is small fighters against the Death Star, they probably don't have the mass to do much damage. In ESB they only had a few evac ships and needed them to evac stuff, not be missiles. In ROTJ the Death Star was shielded and the rebels had a reasonable chance at victory so they wouldn't start sacrificing themselves. Prequel battles were pretty evenly matched. Even in TFA they didn't have a way to ram the Starkiller base, nor a need to. Only in TLJ was there such a lopsided battle with just the right circumstances for this tactic to work and provide a significant swing in the fight.

When you think about it this would actually be very difficult to pull off.

Space is big and ships are small. Ships are a moving target and the velocities involved are high. So hitting from a great distance will be extremely difficult.

From closer range it will be possible for the target to either destroy the rammer first or move out of the way. In The Last Jedi it's only Hux's hubris and slowness to realize what is happening that allows Holdo enough time to line up her ship.

Holdo is further aided by the fact that the Supremacy is vast, by far the biggest ship we have seen so far in Star Wars, 60km wide. Even so, Holdo misses the main bridge and Snoke's throne room (although the latter might not have been externally visible, but the bridge certainly was) and ends up hitting it a little off centre.

why this isn't used as a weapon more frequently, lets say by strapping a hyperdrive to chunks of rock?

Let's make this rock even more effective and add an explosive device to it so it does even more damage on impact. Oh, wait, we've just invented missiles.

So why aren't they using missiles?

The Star Wars universe leans heavily into laser as opposed to kinetic weaponry. The main issue with kinetics is that kinetic energy requires physical mass, so any ship is limited by what ammunition it can carry. You cannot be self sustaining or travel indefinitely if your ammo is a non-renewable resource.

But lasers are unlimited as long as you can generate (or harvest) power.

Power generation is not an issue in the Star Wars universe for day-to-day ship affairs, so it makes much more sense to carry an unlimited amount of laser shots than a limited amount of kinetic shots.

Imagine how many hyperdrives you'd have to build, attach, and destroy in the process. Factor in the misses, and the sheer amount of rocks you'd need to hoard to make this an effective long term strategy.

Also, you'd need more than just a hyperdrive. How are you going to orient your rock correctly? You're going to need several thrusters to accomplish this. 6 thrusters for linear movement in all 3 directions, and additional thrusters for the 3 axes of rotation.

Since you don't want this rock to be manned for obvious reasons, how is this rock going to be steered? You're going to need an antenna at the very least, and the Star Wars equivalent of a probe cockpit for to execute the maneuvers.

Oh and also, you better hope your enemies are near an asteroid field. Or are you going to carry your rock collection around with you? Well now you either need to load them on the ship, or provide your rocks with means of travelling by themselves.

If you keep them on your ship, whenever you release them they're going to be sitting ducks. You'd want them to hit your enemies from unexpected directions, so your rocks need the ability to fly all over the place, so you're going to need to put some sort of power reactor on your individual rocks (note that this presumes you'd have been using some sort of one-time-use battery for your hyperdrive shot - otherwise you'd already need a generator for the hyperdrive).

And then we need to account for how many of these rocks are going to miss their target. If we need to fire 10 rocks to hit once, that is a hell of a lot of work for the amount of damage that a laser could easily cause in less time.

If you want a ballpark estimate of how much ammo is wasted in general miltary affairs: One out of every 250,000 bullets shipped by the US to Iraq/Afghanistan killed an enemy combatant. That's a 0.0004% hit rate.

If the US is not capable of sustaining its own bullet supply, think of what it would take to build hyperdrives, thrusters, probe cockpits, power generators and antennae. You might say "well there's many planets!", but keep in mind that all of this equipment has to be ferried around. The logistical challenge alone would be a nightmare.

You're going to need a lot of hyperdrives.

Oh and also, that's not even factoring in the relative mass difference between your rock and your target ship, which others have already written answers on. I've assumed (for optimism's sake) that adding hyperdrive speed to an object adds enough energy for it to significantly damage any target (no matter the mass/size) that's not in hyperdrive.

I don't think there are many other reasons to use this tactic other than as a last resort. And that was exactly what it was used for in this instance. I'm sure there is a story out there somewhere where it was used once before, those ships are pretty expense so there's no point to do it unless there's a specific reason to. As to your rock and robot theory, I'd assume a hyperdrive has alot of maintenance and requires a lot of processing to use it correctly. To just "strap one on a rock" is probably easier said than done, and most likely needs a stable environment and system to work properly. But then again, this is science fiction were talking about, where anything is possible.