January 1, 1944: Haymaker!August - December 1943
I believe this is the time period historians will look back upon as the beginning of the end for the Japanese Empire. This five month period marked the ascendancy of Allied air power and vital blows that have breached the Japanese inner perimeter. We shall start with the Allied push in the South Pacific.Operation Cleanup Aisle 4
Lae and surrounding areas captured AUG-SEP1943
The capture of these bases has driven the Japanese to the remote north coast of New Guinea. Offensive operations are on hold here due to the law of diminishing returns. Pushing further has been concluded to be a waste of resources. With Rabaul isolated, the IJN/A threat to the South Pacific is negated.
Tulagi Captured 16SEP1943
Tulagi, the last bastion of Japanese strength near Guadalcanal was overrun, eliminating their last chance at threatening the US-AUS supply line.
Shortlands Captured 15OCT1943
The fall of Shortlands (and previously Torokina) removed the last defenses from Rabaul proper. Allied 4E bombers now routinely sweep the ports of Kavieng and Rabaul. This has put a serious hamper on IJN submarine operations, with over 10 SS destroyed in port. Operation Hammerstrike
Operation Hammerstrike, the recapture of Wake Island, succeeded on 11AUG1943. Adm. Nimitz rightfully concluded that gaining the use of Wake during the upcoming assault on the Marianas would be of paramount importance. Throughout the assault on the Marianas, Wake was used as a safe harbor for replenishment ships, a ferry point for aircraft en route to the Marianas, and a resupply point for the CV TFs. Operation Welcome Mat II
A second bombardment was carried out on the airfields of Truk resulting in significant losses (>800) in aircraft. However, the Japanese war machine lumbers on and the losses were replaced in 3 weeks. One wonders how long Japanese industry can keep up with losses of this magnitude...
And finally....Operation Yuletide
The full cost of the Marianas assault for the IJN/A cannot be understated. It may not have been a knockout blow, but they are certainly on the ropes. Japanese air power was close to overwhelming in the early phases. Early intel reports indicate that over 1000 Japanese aircraft were lost in the defense of the Marianas with an Allied loss of roughly 300. The difference was the use of Wake Island as a resupply point. USN CVs replenished their fighter complements at will at Wake, and with a roughly 3:1 margin of victory in air battles, it was only a matter of time before the pendulum swung to the Allied side.
Intelligence found that Tinian was far better defended than originally thought and the assigned two regiments would not be sufficient to take the island. The Tinian invasion has been assigned an additional division and will commence some time in January.
The IJN sortied the Shokaku and Zuikaku in separate TFs to stop the invasion. Thus comes our unlikely heroes: SS Guardfish and SS Hake. Hake torpedoed the Zuikaku a day before she arrived on scene, forcing her back to Tokyo. She eventually sank before reaching port. The Shokaku was torpedoed by Guardfish and was dispatched by carrier aircraft from TF 25.1 supporting the Saipan invasion. This was critical as CAP levels were falling drastically and the appearance of 2 CVs full of trained airmen would have evened the scales against the Allied assault force. The losses would have been much higher if they had not been damaged (which put their flight decks out of action) before reaching striking distance.
IJN subs scored as well, hitting the CV Saratoga and BB South Dakota. They did, however, make it back to Pearl.
The CV Yorktown and BB Alabama received torpedos from Bettys that fought through the CAP screen. They, too, returned to Pearl for repairs, and came back online in December.
IJA casualties were in excess of 30k men, with the 21st DIV completely lost on Guam.
See below for battle maps.