What if Japan just goes after Germany’s scraps after 1931?

They probably won't have to. If Japan goes to war in 1940 the reserve of strategic materials it stock piled OTL in 1941 won't exist. The US simply freezes Japans bank accounts in the the international banks as it did OTL, enact the other embargo. Japan is now cut off from its primary sources of oil, steel, alloys, chemicals, machine tools, half the cargo shipping that serviced Japans ports, ect... Without the reserves built up in the 12-16 months before Dec 1941 Japans industry starts shutting down in roughly 90 days & is collapsing at 120 days, the war fleet runs out of fuel, the winter of 1940-41 sees severe food shortages in Japan, coal shortages, ect.. ect...

However the idea the US is magically blocked from war with Japan is a bit over the top. As I pointed out mobilization is going to start in 1940, the Two Ocean Navy budget would be enacted, 900,000 men were conscripted & plans laid on for drafting 3,000,000 more into the Army. All that was set in motion by the collapse of France, some actions earlier. The US was also fighting a undeclared naval war with Germany in the Atlantic, and occupied 'neutral' Iceland long before any German DoW vs the US. The establishment of the mid Atlantic Neutrality Exclusion Zone and "Shoot on Sight" orders are a useful model for the Pacific. A 200 nm exclusion zone around the Philippines constrains Japanese warships & cargo shipping in the South China Sea. Ignoring that while the US send reinforcements to the PI & weapons, ammunition, & all the other items to the Commonwealth & Netherlands East Indies is kind of stupid for Japan & all to the advantage of the US.
What does Britain do those 90+ days?
 
Britain defends.

One advantage over 14-18 months later is the submarine fleet is not depleted by operations in the Mediterranean. A fair size flotilla of large T class subs can be deployed, with good torpedoes.
 
Doesn't this play directly to the 'bastion Singapore' strategy that the RN crafted after WW1? The Japanese aren't threatening Burma or Malaya via Thailand, China and French Indochina Ittl.

this turns the whole affair into a naval war.
 
Can they actually defend themselves from Japan at that point?

Can Japan actually attack at that point? OTL Japan depended on land based air to attack & land a army in northern Maylasia. As per the OP Japan has not yet acquired air bases in Indochina. Either the Japanese can invade IC first & then establish the air bases and bring in the combat air groups. Or it can try using naval air support to go straight for Maylasia. At this date there are fewer Japanese aircraft carriers, more British warships available, and the more modern aircraft like the Zero are not operational. In the summer autumn of 1940 the only operational fighter plane on the carriers was the A5M. With a maximum speed of 270 mph at 10,000 feet & two 7.7mm MG it was already obsolete after three years service. It also had significantly less range.

There is also the question of how large a ground force Japan can bring together at this point. The armies deployed to the Philippines, Maylasia, and Dutch East indies were pulled together over some six months of preparation. Is there that much preparation in the situation outlined in the OP?
 
Japans Navys finest 1940

A5M copy.jpg
 
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