Thanks for all the reply’s. My question was more narrow than the politics or financial side. I thought I read once where military planners about 1920 came up with a number of 450,000 for a peacetime, active army, as a number that befit a country the size of the US, at that time. This didn’t take into consideration budgets, or policy, just a number. Needless to say, it was simply a paper-plan, and went nowhere beyond military think- tanks.
You'd need a POD involving the US doing worse in a war. Maybe some sort of limited war happens with Japan in the twenties. Doesn't last long but the US doesn't really do that good. The was ends with status quo antebellum but post war their is more funding for the armed services.
What I'm thinking for the Army
Active Duty- 175K active duty. As part of this process after their term of enlistment expires they spend say four or five years in the Reserves
Reserves- Say 75K Men
NG- Say 300K-400K men
The NG and Reserves are maintained at a much higher standard of quality, readiness, training, and thanks to all the WW1 surplus their armed and equipped the same as the regulars. Those pushing for the reform use the "Minuteman" schtick but make sure that the NG is a lot more professional, much more easily and quickly mobilized, regularly train with the Regulars, and otherwise are of much better quality then OTL for the period (where significant portions of NG regiments might drill with literal broomsticks barefoot because they completely lacked rifles or boots.
600K State Militia/State Defense Forces- Of lower quality then the NG but better then the OTL Period NG. Reasonably well armed. Not intended to be deployed abroad but instead to say take over CONUS duties from regulars and NG. For instance they would take over or supplement Coastal Artillery units in the event of War. Also things like guarding key installations and other "lower end" deals. Also man ground based AA in the event of enemy air attack.
Here instead of so much of the WW1 Surplus being scrapped, surplussed, sold off, or sent into deep storage when it could still be used it's distributed across the services to allow or standardization of as many aspects as possible.
Assuming the Japanese War in the 20's doesn't go great and the US is planing on holding on the Archipelago for a while or maintaining some sort of arrangement an earlier reform of the Philippine forces is initiated. The Philippine Scouts are expanded to a full division and a plan is initiated to build a capable regular army of say 5 or 6 well equipped Philippine Divisions backed by another 10 part time decent Philippine NG Divisions. Funding opens up a bit to modernize various fortifications, station another US division in the Philippines and reform and upgrade the existing US forces their. Meanwhile Guam, Wake, and Midway begin long term fortification plans involving among other things potentially permanently stationing a "USMC Base Defense Brigade" in Guam. Fortifications in Guam, The Philippines, Midway, Wake, and Hawaii are all modernized and improved. Among other improvements many of the railway guns that in OTL were constructed or modified for WW1 service but saw service too late are instead of being scrapped moved to the new fortifications. Additional fortified storage facilities are created especially in Bataan/Correggio and Guam to allow for a large garrison to safely supply itself throughout a siege.
Among other things Plan backers manage to get many if not most colleges require some basic military training as part of their curriculum. This is also copied by a number of high schools.
In the Phillipines and Guam facilities are constructed or expanded to allow a number of shorter ranged submarines to operate as commerce raiders and scouts. First the S boats but later newer classes of cheap coastal submarines designed to be cheap to build, deploy, man, and maintain while proving superior to the old S boats. In the Phillipines a number of Sea Ramp facilities are constructed throughout the islands. These generally have some crude sea plane facilities. But a small number of converted Flying Boat/Sea Plan tenders modified from merchantmen are also ordered allowing groups of sea planes/flying boats/ float planes and PT bots to be rapidly switched between islands both for recon and raiding. It's cheaper then building full facilities at every single sea ramp.