Not exactly standard equipment for dive bombers, but the US and Germany used guided missiles against enemy ships with some success before the end of WWII, one of which was enough to polish off the Italian battleship Roma.
Wiki links if I get a chance here in work 
There’s no question that once delivered to contact with the target, a torpedo is more destructive than a bomb.
Is there any assessment of the relative difference in likelihood of scoring a hit between a dive bomber and a torpedo plane?
Once in the water, the American torpedoes were inferior in many ways to the Japanese Long Lance models. But before they even got there, the gyroscopes used to stabilize the American air-dropped torpedoes (I don’t know if this applied to the Japanese weapons or not) had to spin up for two minutes of straight, level flying.
Since the Devastator flew at roughly 100 knots while launching, and the Japanese carriers could make 30-33 knots, and launch angle is generally perpendicular, this appears to present a nearly insoluble problem…flying an arc to reach the broadside of a turning ship you’re only 3.0 times faster than…but 3.14xxx is pi.
Did Devastators ever hit moving warships (as opposed to ships in harbor, such as the Port Moresby attack, or slwo merchantmen)? Did other torpedo planes hit comparably to the hit rate of dive bombers?
In a lot of cases, ships took bombs AND torpedoes. Did dive bombers hit first and slow the ship, setting up torpedo attacks that delivered the coup de grace?
I’ve wondered these things.
Sailboat
From what I’ve read, American torpedo squadrons prefered to attack an enemy ship in a pincer movement, with each division of bombers attacking either the ship’s starboard bow or it’s port bow. If the ship turned in towards one of the bomber divisions (providing them the smallest possible target) they would also end up turning away from the other division (presenting them with the largest possible target). Basically, they’d compensate for their limited maneuverability by ganging up on the target from different directions.
At the battle of Midway, none of the torpedo bombers, including the heavily armed TBF Avengers of Torpedo 8’s Midway Detatchment, scored any hits, but none of them were supported by fighters or dive bombers either (I think Torpedo 6 MAY have had some fighter support, but not nearly well coordinated enough). Of course, this was with relatively inexperienced pilots and the absolutley horrible Mark 13 Torpedo.
My favorite problem with the Mark 13 was that if you scored a direct hit, it wouldn’t explode. The torpedo apparently would strike the hull with enough force to deform the trigger, instead of detonating it. The story I read was that Albert Einstein redesigned the trigger so that the force of the impact would set it off instead of breaking it.
And then, in 44, the US Navy & Cal Tech created The Tiny Tim. Though mostly too late for the War, it would hearld the shape of things to come.
Regarding attacks upon battleships: how would a puny topedo ever sink a battleship? I recall that the main belt armor of the YAMATO was something like 14’ of solid steel! I can’t imagine that a topedo could have much effect against that. I also recall that the YAMATO was sunk by dive bombers-one pilot (reportedly) managed to drop a bomb down one of the ships smokestacks!
I wonder how anyone would know this.
In general, 500lbs of high explosive exploding against a ships hull with the effect of water tamping is going to do a fair amount of damage. I have read that the Yamato suffered from poor quality materials and welding, so a torpedo hit broke apart the armour and caused flooding with aobut 4000tons of water, but I’m not sure how correct this is.
Bear in mind that all battleships were principally designed with protection against heavy-caliber gunfire in mind - the older ones against low-angle gunfire, the newer ones also against plunging fire coming down at 45 degrees or so. Torpedoes were very much second on the list of concerns, then bombs - so underwater was definitely a weak spot.
Hey, the Bismark was crippled by biplane torpedo bombers, even with all it’s thick armor. Sometimes the armor (or the ship it’s attached to) may be built poorly, sometimes a torpedo (or a bomb, in the case of such ships as the USS Arizona hits just the right spot, and I imagine that repeated torpedo strikes, combined with the structural strains of evasive maneuvering (the battleship’s not just gonna sit there while you shoot at it) and repeated bomb hits would affect the overall integrity of the hull and armor.
Plus, as has been said, torpedos get much of their destructive effect from the fact that the explosion happens underwater, effectively turning the torpedo into a shaped charge (unlike the hollow hulls of ships, water does not compress when face with sudden changes of pressure).
A side question, could the running depth of American torpedos be adjusted during WWII? I know modern torpedos tend to run beneath a surface ship and detonate directly under the keel, snapping the ship’s spine in two, so I imagine if you could adjust the running depth, you might hope to have the torpedo strike farther below the waterline…
They could. At least, some of the ones used on submarines could.
Yes, though at least for the early part of the war American and German torpedoes had problems with their depth controls.
Yes. Torpedoes used in WW2 did have a depth setting feature available to them.
The Mk14 was the USN’s submarine deployed torpedo weapon (surface ship was the Mk15, the airdropped was the Mk13), and has gained infamy as to its (un)reliablility.
To explode under a ship (as opposed to a contact exploder), a torp will need someway to know exactly when to detonate. Throughout most of the war, that was intended to be achieved from a magnetic exploder/sensor. (The late war Mk24/27 was an early acoustic model…) Unfortunately, the Earth’s magnetic field is a tad more variable then initially realised, and the torps relying on the magnetic detonators therefore did not function as expected or required. The UK and German torpedoes also suffered in this area, although by 1942 they had the bugs worked out.
Additionally, a poor depth control devise, and a poor contact exploder, made troubleshooting these finicky and complex devices mucho fun. (It was late '43, before the USA began to produce a more reliable weapon.) Further complicating matters, a handful of submarine skippers did acheive success with the poor weapons, encouraging the beauracratic types in the Bureau of Ordnance to circle their wagons defensively.
I do not know if the Mk15 and Mk13 had similar poor characteristics…
In general, the IJN used their TB to greater effectiveness, while the USN had better luck with it’s DB.
It’s worth noting that we won. 
To the contrary, the Yamato was quite advanced for the time, using arc welding and several design innovations that improved structural strength without requiring more or stronger materials.
This is not quite true. A great deal of the pre-WWI design philosophy was around survivability against torpedo attacks (which, amongst other things, led to the development of the destroyer as a class of ship), and that survived into WWII as well. The heavy waterline belt of armour that virtually all contemporary ships wore was designed primarily against torpedo attacks.
The Devastator was a poopy TB though… shorter range (than the Dauntless, it’s teammate) and slow speed (making it vulnerable to AA and CAP).
And the Battle of Midway results may have been interpreted (by the various operations staffs) the divebombing was more accurate.
Also interesting to note that for long range patrols and strikes, the Avenger carried a 500lb bomb. (I presume it was dropped in a shallow dive mode.) This skews some results to make it look like the bomb was a better weapon.
To directly answer the original OP question, the dive bomber seems to have been slightly better:
The dive bomber can arrive over the target area, above cloud cover. (For the chance at surprise.) The TB must drop to 75-150 feet of the sea surface.
Once the DB “pushes over”, it’s a tough target to hit. Even with dive brakes, the dive bomber can exceed 300 MPH. The TB must fly at 100 MPH (a little faster for the Kates) when the torpedo is released, or it will break up when it hits the water.
The target has a tougher time “dodging” a bomb. (Make the pilot miss by scaring him with flak.) The pilot can adjust the “aim” of the weapon up until about the “pull out” altitude (of 2500 feet, IIRC).
The torpedo bomber drops his weapon at a distance of 1000 to 2500 yards of the target. (Thats a 2/3 to 1.5 miles. Dang close. You can see the whites of their eyes.) Further out, and the target, assuming it’s under power, has more time for course changing. Even so, a 30 knot weapon takes a minute for every 1000 yards it must travel, if my math holds up. A ship moves almost as far in that time. (Most capital ships being only 700 or so feet long.) Tricky shot to make.
The disadvantage of the bomb (compared to the torp) is that it usually doesn’t let water into the hull. It can start fires. And if those fires get too big, then the ship has to be abandoned. But (like the USS Franklin in 1945) if a trained crew is allowed to fight the fires (and the ship doesn’t lose power to it’s fire mains), ships have survived an impressive amount of punishment above the waterline. (Look at some photos of the US destroyers surviving Kamikaze damage. shudder)
Well, here’s the Staright Dope on Yamato’s armor. The torpedo belt was 16.1 inches…not feet. Note that the turret faces were considered impregnable to the fire of other battleships at 25.6 inches.
The cite calls Yamato’s steel quality “inferior”. That’s a comparative value to other high-end battleships. Battleships generally used very strong armor class steel; stronger and harder per inch than the steel used in other applications.
It’s been said that the American Iowa class ships (smaller than Yamato but very modern for their day) are the likeliest man-made structures to survive a nuclear near-miss (nothing, presumably, would survive a direct nuclear hit).
Despite this enormous strength, not all areas of the ship are armored. Compromises havbe to be made; these things actually floated, remember. Weak spots existed without 16" of armor-qaulity steel belt, and even the armor could be broken under heavy and precise attack.
Sailboat
Good reference: the YAMATO and MUSASHI were the heaviest battleships ever built. Yet, they were only of minor utility by 1944. The Japanese would have been better sereved to have built 4-5 carriers instead. Battleships required enormous crews (to service the big guns)-were they ever worth it? Seems to me a carrier could provide much better striking power, at a much lower cost!
I partially agree with Cerowyn here. The development of the Dreadnought design was in direct response to the torpedo as a weapon.
What is the best was to survive a torp hit? Don’t get hit by one.
What is the best way to avoid torpedo boats? Shoot at them (and sink them) from outside torpedo range.
What is the best way to get hits at extremely long range (where spotting fall of shot is more difficult)? Salvo firing your main guns together. Get rid of the unneeded intermediate calibre weapons (as they will only confuse spotting).
The “all big gun” ship was born. The best defense is a good offense. (At least in this case, a bigger, and longer ranged, gun.)
In 1900, the British fleet was conducting gunnery shoots at 5,000 yards, or so. In actual battle, the ranges had crept up to 15,000 yards…
The airplane could not be outranged… except by other airplanes.
The part I don’t agree with was the heavy waterline armor. That was intended to prevent low trajectory shells from pucturing the waterline. Not torpedoes. (With typically run 10 feet or more below the surface.) Sure, if a torp running on the very surface smacks a 14 inch steel armor plates, it just leaves scortch marks.
Anti-torp defenses typically two or three 1 or 2 inch steel bulkheads, enclosing watertight voids, to mitigate explosions. Extending the main belt to the keel would involve investing way too much displacement to protection, and leave little available for other stuff… History and Technology - Torpedo Defense Systems of World War II - NavWeaps
But I believe the Japanese were limited by treaty in the number of ships they could build. This was yet another sore spot for the Japanese that contributed to the decision to fight. It was also why the Yamato and Musashi were so BIG. With a limit on the number of ships, the IJN wanted as much fighting power per ship as they could get.