Introduction:
Marie de Sevigne quipped that “Fortune is always on the side of the big battalions,” and in the 20th Century, head to head Great Power warfare was typically decided by the weight of industry. WW1, WW2, and the Cold War support that assertion. The Russo-Japanese War is the salient counter-example that is the exception to the rule. Great Powers were often defeated in colonial warfare after WW2, but that is a topic for a different discussion. This discussion will look at War Plan Orange (WPO) through an industrial lens so to speak and see if the simulation War Plan Orange plausibly recreates the industrial consequences of a Great Power war in the 1920s between Japan and the United States.
Economic Estimates: How would a WPO Effort compare to WW2?
First, the USA had a vastly larger economy than Japan throughout the period in question. This is shown in Table 1 below.

Table 1: Comparative Economies (Constant billions of 1990 Dollars)
Source, Angus Maddison @ http://www.ggdc.net/maddison/
Interestingly, this data shows about a 6:1 disparity in relative economic size between the USA and Japan in the period in question. By 1941, this had dropped to 5:1, but US production soared during WW2 while Japanese production essentially stagnated.
In the case of Japan, the numbers tell a pretty straightforward story. In WW2, Japan operated essentially isolated from other economies. There was some technology transfer from Germany. The 1920s economy would support roughly half the output that Japan could put forth a generation later. In the WPO game Britain is a belligerent so the WW2 isolation would be recreated. Under various house rules, a questionable assumption is made that European colonial powers would continue to trade with Japan during a war with the USA, but that assumption does relieve the Japanese player of a crucial resource concern as long as he can deny the USA an offensive base in the Philippines.
During WW2, the USA invested about 30% of its war effort in the Pacific Theater. US spending on the war peaked at about 37% of the GDP for 1943-1945 with 1942 as a bridge year with 17% of the GDP going to war production. With the 30% figure for the Pacific war, that works out to 11% of GDP or about $100 billion to $200 billion per year (depending on whether you’re talking of 1942 or 1944). What that buys you in way of combat power can be seen from studying the order of battle for War in the Pacific (WitP). However, in WW2 it is clear from the historical record that serious naval rearmament started as early as 1939 so the deliveries of long-lead time items like aircraft carriers and battleships in 1943 had their origins far before the first shots were fired in 1941.
In the case of WW1, the US was continuing a naval construction program of 2 battleships per year, only prudent given the uncertain outcome in Europe, and went to war in 1917 only a matter of months after Wilson was inaugurated for his second term after campaigning on a platform of having successfully kept the USA out of WW1. Consequently, although the USA was contracting munitions production for the Allies, the US military was much closer to a “standing start” in getting to a war footing compared to the mobilization in WW2. US military spending for WW1 actually peaked in 1919. Much of the construction started in WW1 was only completed after the war. In some cases, like the USS Narwhal (also known in WPO as Submarine V5), the submarine was authorized prior to WW1 and was only commissioned in 1930. For 1919 I have contradictory numbers which indicate military expenditures of about $11 billion and total government expenditures of $11 billion, with military spending at 60% of the total US budget and a $70 billion (in 1929 dollars) US economy. Working through the algebra, that indicates a US mobilization level of 9% to 16% of the total economy compared to the 37% seen in WW2. It is a conjectural to speculate if the USA would have eventually reached its WW2 mobilization levels had the Great War endured several more years, but existing data does show that even in the peak year of 1919, there was a sharp decline in government expenditures during the 2nd half of the year as the US military demobilized. That leads me to conclude the 16% figure is a reasonably conservative floor for the ability of the USA to mobilize for a prolonged war in the 1920s.
The premise of WPO includes a breakdown in the post-World War I disarmament talks. Under those circumstances, Japan continues to build up its fleet for a conflict that is described as inevitable. The USA also continues to build capital ships and during the course of the 1920s, twelve ahistorical battleships or capital cruisers join the US Navy, evidence of continued large expenditures for naval armaments. The WPO scenarios also include the historical building programs for the “S” class submarines, Omaha class light cruisers, and various Japanese light cruisers.
In the early scenario, the Allies would have recent memory of WW1 to guide them, so one would think that the government would have been able to match the sort of mobilization found in WW1. Furthermore, given the lack of aircraft development from WW1, the overwhelming major of funds would end up being invested in naval and army expenditures. Taking the investments times the GNP, then that works out to about $100 billion dollars/year, or roughly 50% of the historical Pacific Theater investment in WW2.
In the late scenario, there is a larger pool of wealth for the American military to draw from, thanks to the economic growth in the 1920s. The aircraft industry had matured a bit so there would be more in the way of aircraft to absorb spending. I think the number here is best estimated as between the WW1 and WW2 mobilization levels but still much closer to the WW1 level. If we figure it at 20%, then that gives us $156 billion dollars per year or roughly 75% of the historical Pacific Theater investment.
So in summary, we should expect to see a US effort in the early scenario that is roughly half of the historical WW2 effort. In the late scenario, where the US would have a larger economy to exploit, three quarters of the historical WW2 effort. Since the aircraft in the 1920s are more primitive and less expensive than their WW2 counterparts, that means the investment will show up in warship construction and ground forces.
More to follow . . .