I was going to nominate Patton.
It’s not so much that he failed to win that massively lopsided engagement, but that getting into it in the first place was almost entirely the result of Custer’s arrogance and ambition.
It was obvious a bad decision but as I said before there were extenuating circumstances. Custer was experienced at fighting Indians. He knew that trying to pin down Indians in a battle was usually more difficult than fighting the battle itself. Most Indians generally preferred to fight with guerrilla tactics - strike where their enemies were weakest and avoid contact with heavily armed soldiers.
So when Custer learned the location of the Indian camp on the Little Big Horn his biggest concern was to attack in a way that prevented the Indians from escaping.
Custer’s mistake was deciding to not take the time to do more reconnaissance. He knew the approximate size of the Indian camp but assumed it was a normal camp, which would have been mostly civilians with a minority of warriors. Custer also thought he was fighting only Lakotas and he had good information about how many warriors the Lakota had. Based on what he could knew, he estimated he would be facing approximately 800 warriors. American soldiers had won battles against Indians at 4-1 odds via surprise attacks in the past.
What Custer didn’t realize was that he wasn’t facing a normal camp. This was a battle camp. There were some civilians present but this camp represented a concentration of warriors from several tribes. There were two to three times as many warriors in the camp as Custer thought and the odds against him were around 10-1.
Custer fell into a trap-his scouts failed to inform him that his Indian foes were BETTER equipped than his soldiers. The Lakota warriors had Henry rifles with brass cartridges-they could fire at a faster rate than Custer’s men. Also, the US soldiers were issued defective cartridge belts (cheaply tanned leather)-the chemicals leaching out of the belts corroded the copper cartridges carried by his men-which caused many trooper’s rifles to jam-many men died because they were trying to clear a jammed cartridge.
Custer wanted to have the battle on the 100th anniversary of US Independence- hardly a sound decision.
Anyone interested in this topic ought to take the time to page through the Worst Military Leader thread Tom Scud linked to above – there are some entertaining discussions there.
While I agree McClellan was risk-averse, he planned two large-scale amphibious movements to land in the rear of an enemy force, and executed one of them without loss (well, the landing part, anyway). While not completely analogous to Inchon, that’s close enough that your statement raises my eyebrows.
I’ve read assertions that Custer thought the warriors were away from the camp, and he was eager to get in there and kill defenseless women and children before the warriors returned.
Burnside is a good choice, but for one thing - of all the truly awful generals out there, he’s one of the few who knew he was bad at generalling - and said so. 
Mach Truck, I agree that going against the will of the person in charge is especially dangerous- for a start the President is the one who knows the whole situation- not necessarily the General who may only be seeing a fragment. From what you say Power could be potentially terrible- I just am not convinced that performed an action that would confirm the potential.
I think Eisenhower was mentioned above as not being a field commander of any note and that is probably true. However as a supreme commanding general he was very good and was not afraid to get rid of top commanders who he believed weren’t performing. I have read that he sacked 5 generals: Patton sacked none.
And I think there are a couple of types of failure (or worst) emerging here. There are the generals who made one stupid blunder that cost them dearly (such as Custer if you want to include him as a General) and were killed or removed, or those who were allowed to continue on and create a series of blunders.
A couple of other points in Burnsides’ favor – he was uncomplicatedly loyal to his government and his superiors, and physically brave in the face of enemy fire.
Some of his plans started out pretty well, too – he stole a march on Lee to get to Fredericksburg…but then he was unprepared to cross, and ultimately persisted in foolish frontal attacks one he’d lost the element of surprise. The Crater battle plan was decent, and the troops well-trained for it – but when his choice of units was overruled (Meade was afraid that leading with the black divisions would be seen as using them for cannon fodder) he gave up entirely, and chose Ledlie, the worst of his subordinates, for the role by drawing straws. I think perhaps his greatest flaw was his tendency to sort of throw his hands up and stop trying when initially thwarted.
Fredendall has been rightly criticized for his failure, but an additional black mark against him is his insistence on bizarrely obscure, entirely unintelligible lingo in his orders.
[QUOTE=Wikipedia]
Fredendall was given to speaking and issuing orders using his own slang, such as calling infantry units “walking boys” or artillery “popguns.” Instead of using the standard military map grid-based location designators, he made up confusing codes such as “the place that begins with C.” This practice was unheard-of for a general and distinguished graduate of the Command and General Staff School, who had been taught to always use standardized order procedures to ensure clarity when transmitting orders to subordinate commanders under the stress of combat. Fredendall’s informality often led to confusion amongst his subordinates, and precious time was lost attempting to figure out his meaning.
[/QUOTE]
I’ve seen parts of his Kasserine Pass orders quoted and they are comically inarticulate, except for the fact that men died as a result.
I’m curious - do you consider General Curtis LeMay a war criminal? The man killed far more civilians, and burned far more homes, than Sherman ever did.
Myself, I think that’s an excellent argument to be made for LeMay - as he himself admitted - but the argument for Sherman is weaker. He burned homes; but so far as I know, the idea wasn’t to burn people in them. He wanted to break the will of Georgians to resist - not an unworthy goal, as they’d fought for treason and slavery for years. But the man seemed to take civilian casaulties seriously.
Though I’d keep him from the top of the list, purely because he did know perfectly well that he shouldn’t have command of the army. The President asked him to do it, so he did his duty - but the man was able to accurately assess his own lack of qualification for the role. Plenty of incompetent people can’t do that.
Heh. This makes me grin a little; I live a few blocks from Ft. McNair, in DC.
I’m no expert, but I don’t think the Indians get the credit they deserve for wiping out Custer’s command. Sure, Custer acted rather rashly, and flew headlong into a larger force, but he was basicly using tactics that had largly worked pretty well up to that point.
The difference at Little Bighorn was that the Indians were ready, knew he was coming, and determined to put up a fight. They fought well, and*** they won* **the battle.
No, they didn’t plan on killing the defenseless women and children (at least not most of them). The plan was to ride in on a surprise attack and capture as many women and children as possible. Then these captives would essentially act as a “human shield”. The Indian warriors would be limited in their ability to shoot at the soldiers because their own family members would be alongside them.
Okay, but imaging Custer saying “Kill defenseless women and children? Oh no, I’m not going to kill them. I’m going to use them as human shields!” makes him sound like a Bond villain instead of a war hero. 
Yes, I’m not saying Custer was winning any humanitarian awards for this scheme. But my point was he had a plan. It didn’t work obviously but it’s wrong to think that Custer just blundered himself into a massacre.
A trivia sidetrack: Custer was a pioneer aviator. During the Civil War, the two armies experimented with using balloons for aerial reconnaissance. Custer was one of the officers who volunteered to go up in a balloon to look over Confederate positions.
Nitpick: I think the correct term is “aeronaut”.
Aeronaut may be more precise but aviator isn’t wrong. An aviator is somebody flying in any type of aircraft. An aeronaut is somebody flying specifically in a light-than-air aircraft.
Westmoreland was a good and decent man who, by all accounts, was a product of his environment. He gladly would have “won” the war if it had been possible, but he was hamstrung for a lot of reasons and probably couldn’t have succeeded anyway simply because that war was singularly unsuited for the post-World War II US military.
I’d say Paul Harkins, his predecessor, was much worse. Not only was he completely out of his depth, he was a shameless liar to boot, and his lies made things much worse. David Halberstam absolutely and rightly savaged Harkins in The Best and the Brightest, and while he wasn’t too big a fan of Westmoreland either he didn’t give him nearly as much venom.
Also, depending upon what makes a General “bad”, there have been numerous generals busted down to a much lower rank for crimes committed while commanding non-combat forces, like Thomas Fiscus.
Has anyone mentioned Benedict Arnold yet? I mean, he was the only out and out traitor.
Not the only one. I already mentioned Charles Lee and there was also James Wilkinson.