We didn’t need the Philippines for that. Once we took Iwo and Okinawa, Japan was finished. All we needed to do was get within bomber range and we did that from Mariana Islands
Iwo Jima is tiny and not in the right place to effectively interdict Japanese shipping coming from the East Indies.
Okinawa would have been a much tougher fight if the oil coming up from the Indies had not been interdicted months before the invasion with all that extra gas for kamikazes.
“...Once we took Iwo and Okinawa, Japan was finished. All we needed to do was get within bomber range and we did that from Mariana Islands.” [AppyPappy, post 33]
This is justification after the fact.
When US forces were attacked at Pearl Harbor, very few long-range bombers existed beyond the concept/design stage. Air bombardment was not a proven strategy (it still isn’t, to hear some of the more mulish, backward-looking apologists for the senior armed services).
The Allies knew little about Japanese intentions and capabilities. The “best” strategy for fighting back was guesswork; no one knew exactly how any of it could be accomplished.
The success of the US B-29 program was an iffy thing through a good share of series production. Designed in 1939, it was revolutionary: range extended by 60 percent with double the warload of any previous US bomber. It was beset by problems early on, causing delays and ultimately costing more than the Manhattan project.
No other Allied bomber then operational could have flown from the Marianas to Japan and back. Earlier attempts to employ B-29s - such as strikes from forward bases in China - had proven infeasible. The Aleutians were under consideration for forward basing.
Not even the B-29s could hit 100 percent of Japanese targets from the Marianas: parts of Hokkaido were beyond the range. The B-32 might have done it, but was never tested in action that way. The B-36 could have, but the war ended as prototypes were under construction.