I do wonder what the Japanese high command is thinking right about now.
If I had to guess, they are realizing they will have to make an important decision. The desctruction of the Sagakuchi Detachment means they are running one month behind schedule. The OOB in Ambon and geography makes is plausible that the first attempt to seize the island will fail. Thankfully for the Japanese the Allies cannot project naval and air power that far north in January 1942, so their naval assets will be safe.
Even in OTL the Japanese were aware that allied reinforcements were arriving at the DEI. Now the Allies have even more breathing space and lots of assets will be arriving at Java with every passing week. The Japanese also know that the British do not have an active front in Mediterranean, so they will anticipate the relocation of RAF squadrons. Once they realize that Malaya is not going to fall any time soon, they will have little hope of closing off the western approaches to Java.
So, they have two choices if they want the javanese and the sumatran oil fields:
i) Fight a war of attrition by capturing Timor and Bali and utilizing land-based air power to slowly degrade the defences of Java for a successful invasion. It will take time and the western approaches will be safe for the Allies to continue pouring assets.
ii) Use the Kido Butai in the closed Java Sea to suppress the many airfields in Java. No mere raid, but proper suppression. Perhaps to send first the Kido Butai to attack Darwin to destroy shipping and airfield, same as in OTL.
Neither of the above is a good choice in my opinion, but they cannot do anything else.
The problem is that the Allies have now the capacity to shift enough fighters and bombers to the DEI. In the case that they would use HMS Formitable
for a last Club Run to ferry aircraft from Port Sudan (alternate ending of the Takoradi route after December 7th), then there is enough time for HMS Ark Royal
as well to do a Club Run before the IJN is ready to attack Java. In OTL 40 more Hurricanes had arrived with the aircraft transport Athene.
In OTL late February, Java was expecting 20 P-40s, 10 A-27 dive bombers, 8 B-17s and50 Hurricanes. These were either re-routed after the landings, lost at sea or were overrun. Convoy MS.5 carried 65 P-40s along with pilots, ground crew, tools, spares, ammunition and vehicles. On February 17th it was sent itself to India. Only days afterwards it was sent back towards to Java and we know what happened.
In general, according to the "Allied Defence of the Malay Barrier":
On January 26 General Wavell announced that 320 fighters were en route to the East Indies. Another 320 fighters would reach Java no later than April 15 in addition to other reinforcements.
I wonder, without an active desert campaign, how faster the british portion of these fighters will arrive.
The australian brigade in Ambon means that the raid against Darwin will take place a bit later. There will be more american fighters and bombers in Darwin. "Strategic Planning for Coalition Warfare, 1941-1942" mentions that:
In mid- March the force had twenty-six B-17's. Of these, twelve were then in shape to operate, as against an assigned strength (for two heavy bomber groups) of eighty operational planes plus reserves. There were only one or two B-25's, not in commission, as against an assigned strength (for two medium bomber groups) of 140 operational planes plus reserves. Light bombers and
pursuits were more nearly up to strength. There were forty-three A-24's and one or two A-20's in Australia, of which twentyseven were operational, as against an assigned strength (for one light bomber group) of fifty-seven plus reserves. There were about 350 pursuit planes (P-40's, P-400's, and P-39's), of which half were operational and the rest to be repaired or assembled
In TTL Darwin will have teeth. Java will have very sharp teeth. Nagumo won't be happy.