This is a great question!
First: timing is everything. if Center Force had simply cruised by Taffy 3, which is entirely plausible, it would have reached the Gulf at about 11 am. Taffy 3 was about 80 miles from Homonon Island, which is at the mouth of Leyte Gulf. At 20 nautes, it should have reached its objective in 4 hours. In real life, Kinkaid learned of the presence of Center Force at about 07:00. Even then, he was unwilling to release any ships to engage Center Force until 08:15. He would have to organize his forces, which had been “mopping up” Southern Force, rearm them, and determine a plan of attack. The WV, perhaps his most effective battleship, had damaged screws and could make only 10 nauts. It’s isn’t like Oldendorf’s ships were already there. many had chased Admiral Shima’s ships out of Suragao Straight. Kinkaid was wary of leaving his position until he could be certain that Shima’s force was not going to turn around, as did Kurita, and head back to the Suragao Straight. Maybe, Oldendorf can engage Center Force in a shootout by 1 pm? Remember, in real life, he intended to send only 4 old battleships, some cruisers and destroyers to meet Center Force. Such a force would be outgunned by the IJN. However, before Oldendorf arrived, the Taffys would harass center Force, causing damage, torpedoing/bombing ships. It isn’t a matter of whether Center Force is destroyed, its a question of when? How long will Kurita have to destroy the Landing? Kamikazes would inflict serious damage on the Taffys and Seventh Fleet. It would be a bloody mess.
Second: the surprise factor is huge. Halsey can never get to the fight. If Taffy 3 had not spotted Center Force, Kurita’s ships would simply have sailed into Leyte Gulf. Admiral Kinkaid, who assumed Task Force 34 was guarding San Bernardino Straight would have left it unguarded. Halsey, who wrongfully assumed that Center Force had been driven from the fight would be 400 miles away hunting down the Japanese decoy force. His planes would be out of range to attack Center Force.
Can you imagine the look on Americans’ faces at Leyte when the Yamato and 3 other battleships, 8 cruisers and 11 destroyers sailed into the Bay unopposed and without announcement? That would have been a Holy F**k moment! I imagine sailors would probably have more choice words. Reaction time would be zero.
Third: much damage would be done. Consider what damage could be inflicted by Southern Force. Give it two hours without opposition. It is A+5 (A Day, as opposed to D-Day, plus 5 days, or October 25, 1944). I have read elsewhere that there were no transport ships there and that American forces had advanced beyond range of naval artillery - WRONG!
The Navy was still in the “Attack Phase” of consolidating the Landing area. There were many transports there on the 25th. Actually, more tonnage was unloaded on that day than the two previous days (11,140 tons). 139 transport vessels were unloaded by midnight of 10/25/44. Many of those were held in San Pedro Bay during the battle. They would have been sitting ducks had there been no advance warning of Center Force coming. Even then, San Pedro was no safe haven. In my opinion, it could have been a disaster.
American marines, soldiers, and sailors would have been in striking distance of 4 battleships, including the mighty Yamato. Leyte Island is approximately 20 miles by 60 miles long. The Yamato can fire 18.1 rounds over 20 miles. Unless I am mistaken, the majority of American forces were within 6 miles of Leyte Beach, many engaged in combat or engineering operations. Would naval fire have been effective on American positions? When used by the USN it was. Well entrenched Japanese forces at Dulag, a stronghold, had been driven away, among others, so why wouldn’t the IJN return the favor? There were many targets for Kurita’s guns. By midnight of 10/25 (A+5), 80,000 troops and 81,000 tons of supplies had been put ashore. Consolidation of the Landing area would have been halted. For examples, the US was linking roads and setting up airstrips, such as at Tacloban. Equipment/supplies would be destroyed. Airstrips could not be completed. Other construction would stop. Many transports would have been destroyed, making resupply nearly impossible, maybe for months. Regarding the airfield of Tacloban, even on 10/25/1944, it had not been completed. One report was that 20-25 of the first 66 planes to land there that day crashed and had to be pushed off the field into nearby waters.
Fourth, there may have been an impact on the war. What effect would it have been on the War? That is a big question. Remember, the Sho Plan was not merely a naval engagement. The Japanese army and air forces also had roles, which they carried out dutifully. Their effectiveness was degraded dramatically by Center Force’s failure. However, had Kurita driven his force into Leyte and blown the hell out of everything he could, their effectiveness would have been far greater. There may even be a threat of putting the issue in doubt.
So, what if Kurita wreaked havoc on the Landing and killed thousands of Americans, sank many ships? Most likely, all of Kurita’s ships will be destroyed. The news will not be about our losses, but it will be about how the Japanese Navy was gloriously sunk in one day by Admiral Halsey and Admiral Kinkaid. Remember, there were no reports about the heroism of Taffy 3 for almost 10 years after the battle, so don’t expect losses of transports to be reported, even with the lives of thousands of Americans lost. It was not until Bull Halsey began writing his autobiography that all hell broke loose and people began wondering the answer to your question. A Naval Study of the Battle of Leyte Gulf omitted the Battle off Samar Island. No one wanted to embarrass American icons.
Maybe, the battle would have an effect on the upcoming Presidential election a few days away? I really don’t know. Many have speculated, but how could anyone know? Then, again, it likely would have some impact on prosecution of the war and conditions of surrender. Don’t know what they would be.
Thank you for a great thread.