see hed. Something about Perceval in the Pacific?
Maybe Battle of Brest- liberation of the French channel ports in 1944 took longer than thought and Paris was liberated quicker than expected.
The whole Italian campaign was probably a disaster although initial Ultra intercepts indicated Hitler would abandon it- he changed his mind. The Anzio landings were mishandled, giving us Churchill’s pungent remark that he thought it would be a wildcat, not a beached whale.
The bombing campaign was mishandled with both British and American commanders refusing to admit it wasn’t working and not targeting specific targets such as oil, Ruhr dams or ball bearings enough.
Pacific? Was Okinawa necessary? Others have argued that returning to the Philippines was more moral than military.
Probably better suited to IMHO rather than General Questions. Moved.
samclem, moderator
Maybe the delayed reaction to messages received of an impending attack on Pearl Harbor would qualify, but I guess that was the error of government officials.
Maybe Kasserine Pass?
By-passing some of the Pacific islands? Okinawa may be a good example.
Maybe MacArthur’s defense of the Phillipines?
Doug MacArthur getting caught with his aircraft on the ground in the Philippines despite some 13 hour warning after the attack on Pearl Harbor has to be up there as one of the bigger failures strategically. He had a chance to launch a first strike on the Japanese forces in Formosa and failed to take advantage of the opportunity.
On a tactical level, how about the Battle of Savo Island?
The Allied fleet protecting the landings at Guadalcanal failed to spot an approaching Japanese fleet that proceeds to sink 4 Allied heavy cruisers and kill over 1000 sailors with the loss of just 58 Japanese lives. The only good part was that the Japanese withdrew rather than pressing the attack home against the unprotected transports and freighters supporting the landings. One of the worst defeats the US Navy was to suffer.
Kasserine Pass is an absolute study in awfulness, a defeat so lopsided it caused a complete restructuring of the Allied command structure.
Being over 2 years late?
This time of year The Hurtegen forest comes to mind. Lots of wasted lives and no real objective other than the Roer Dams. A much over looked battle.
A month from now and seventy years ago it was overshadowed by a much bigger blundered or gamble on the axis side.
MacArthur letting his air force be destroyed on the ground.
Kassarine Pass.
Ike agreeing to Operation Market Garden.
The USN’s Mark 14 torpedo.
Keeping Mark Clark employed, whose tunnel vision in being the one to capture Rome made an already difficult Italian campaign even more difficult. See Operation Diadem, what an asshole.
Ignoring Ultra intercepts concerning German build up in the Ardennes.
Not a battlefield blunder per se, but allowing the Morgenthau Plan to get out. On a similar note, FDR calling for Unconditional Surrender in January, 1943.
Admiral King ignoring the advice of the British on implementing the convoy system in the Atlantic, as a result the U-boats had their “second happy time”. Not implementing coastal blackouts, either, so ships are nice targets against the lights of the shore.
TURKEY TROTS TO WATER GG FROM CINCPAC ACTION COM THIRD FLEET INFO COMINCH CTF SEVENTY-SEVEN X WHERE IS RPT WHERE IS TASK FORCE THIRTY FOUR RR THE WORLD WONDERS
“That son-of-a-bitch Halsey has left us bareassed!” - Sprague.
Halsey gets a lot of stick for chasing the bait and leaving Taffy 3 bareassed at Leyte Gulf, maybe other admirals would have done the same, maybe not…but at the end of the day his job was to cover the ground forces, which he could hardly do chasing carriers off in open sea. Oh, and not telling Seventh Fleet that he was leaving!
A lot of bad decisions have already been mentioned. I’d add the invasion of Palau to the list. It was a battle fought almost as an afterthought. It was thought the island was lightly defended and could be captured easily and quickly and used as an airfield.
But the Japanese had been up a strong defense on the island and it took over two months and eight to ten thousand American casualties to take the island. The strategic value of the island wasn’t worth the cost.
Iwo Jima. Unnecessary battle.
Does anyone know how/why this happened? Is there any backstory?
Worked out pretty well for us! 
I was off on time, MacArthur had about 9 hours of warning.
In short, the attack on Pearl Harbor occurred at about 3am Manila time and the Philippine command was alerted within a half-hour or so. The Far East Air Force under General Brereton recommended launching an immediate attack against Japanese bases on Formosa. He was turned down by General Sutherland, MacArthur’s Chief of Staff.
The Japanese had expected to launch at around 2:30am and attack just after dawn. Due to fog, their aircraft were grounded until 9am or so and the attack on the Philippines didn’t occur until noon. Saburo Sakai would recall the Japanese fliers were afraid American bombers would arrive and hit the bases in a preemptive strike.
MacArthur never authorized the strike and his reasoning was never explained. He claimed that nobody ever asked him for permission to make the attack. The more likely explanation is MacArthur, at the urging of Philippine President Manual Quezon and disobeying standing orders to the contrary from the United States, was unwilling to violate Philippine neutrality without an attack on the Philippines itself. As it was, MacArthur’s indecision led to a paralysis in his commanders that allowed about half of his aircraft to be destroyed on the ground in the opening minutes of the campaign.
We will never likely know the full backstory. Unlike Admiral Kimmel who was court-martialed and cashiered for the failure to anticipate the attack on Pearl Harbor, Army Chief of Staff General George Marshall decided to cover-up MacArthur’s utter incompetency and even, against the advice of Eisenhower, awarded him the Congressional Medal of Honor for his defense of the Philippines.
For longer, better researched:
http://www.militaryhistoryonline.com/wwii/articles/macarthursfailures.aspx
One of MacArthur's biographers, William Manchester, said there is always a "yes, but" in every in every MacArthur battle. The defense of the Philippines lasted longer than any other Allied territory.
The OP mentioned “Perceval”. That is probably Arthur Percival, British commander of Singapore, whose loss Churchill called the worst in British History. Sending the battleship Prince of Wales and battle cruiser Repulse out with no air support (the carrier Indomitable had run aground in the Caribbean) was a bad idea.
I was curious about this because the OP specified he was looking for American military mistakes.
This time of year The battle of Hurtegen Forest comes to mind. Great amount of casualties with no real objective other than pinning down German forces and to capture the Rur dams.
A very overlooked battle in WW2.
Don’t know if I would call it a mistake or like most pointless battles more of a blunder.
Overshadowed by a mistake, gamble on the other side one month and seventy years ago today,tomorrow.
OP here. Yes, it was stupid. I glanced at the Percival reference, wondered about US, and mainlined all over SD.
Although now that I’ve been reminded, more to OP, can anyone think of a case where such a politician of such high rank in the US has commented negatively–to put it mildly–about a US military battle? Especially one within living memory?
Knowing US pieties, the idea strikes me as impossible.