At the fundamental level, there are only two requirements to do this: Withdraw from the London Naval treaty and get invaded which lets you activate the Homeland Defense Emergency Act.

Note: This is not standard gameplay and will greatly disrupt the rest of this playthrough

Step 1: Go Continue the New Deal

Step 2: Under events, select "Withdraw from the naval treaties"

Step 3: When the UK issues "a stern warning" choose to backdown

Step 4: Don't back down, let the mission expire. (This will cause some of the signatories to declare war on you, so be prepared)

Step 5: Let yourself get invaded by losing a core state

Step 6: Save up 50 pp and activate the Homeland Defense Emergency Act


Congrats! You have now jumped to War Economy, Extensive Conscription, removed the Great Depression debuff, and set a base of 90% war support.




Now, have fun fighting France, Japan, and/or the UK. With your starting navy, you should easily be able to take them out, one by one.

First, an explanation of how this all works (and please correct me in the comments if I've made any mistakes or any updates change any of the following):

The Homeland Defense Emergency Act allows you to instantly increase your economy, conscription, war support, fix the great depression, and a bonus 20% attack and defense on core land. It requires 50pp, only works for defensive wars, and you can't be in a civil war. You have to lose a core state to be able to use it.


The London Naval treaty restricts certain countries (signatories) to a maximum cost for cruisers, carriers, and other capital ships. The starting countries include the USA, UK, France, Italy, and Japan.
Normally, fascist nations can/will cheat (partially increasing the cap) and eventually abandon the treaty, leading to an event ("Escalator clause invoked") for those that haven't abandoned it yet. It also gets voided once World Tension hits 75% or two majors go to war.


The game checks naval strength by the number of your capital ships compared to the UK's navy. If you have 80% of the capital ships as the UK, you are threatened by the UK to scuttle your ships until you're once again weaker than them. The US starts with an extremely impressive navy, more than enough to match the Royal Navy.


Leaving the treaty costs 150 PP and needs to be done quickly, which is why you should take Continue the New Deal as your first focus. This allows you to leave before the Second London Naval Conference finishes.



The UK will quickly notice that the US Navy has quite a few capital ships and will issue a warning for the US to back down. Ignoring them only gives the UK a wargoal, which in my experience they never use. By agreeing to back down and then failing to do so, you invite the other signatories to also declare war on you. In my experience, Japan and France will instantly declare war on you. This gives you some options on where to focus your forces.


Japan will quickly naval invade the Pacific, given the opportunity. The HDEA only works for core states, so I'd suggest either letting them take Attu Island after coring Alaska or letting them take Hawaii. This is fairly RNG as to where Japan chooses to invade, so be aware that this isn't 100% reliable.

France has fewer Pacific holdings, but holds a fair amount in the Caribbean. You can core Puerto Rico and let them take it, allowing you to activate the HDEA this way.

Finally, you have the faster, pro version: using the Canada approach. In my handful of tests, the UK doesn't declare war on you even after France/Japan does... unless you naval invade the minor French holdings which border the UK. Once they border you, they'll declare war on you, meaning you can go to war with Canada (as they're in the same faction) if the UK doesn't call them in instantly. Allow the handful of Canadian divisions to trickle in and take a state, activate the HDEA then blitz into Canada before the UK can land any troops.

I've done this tactic a handful of times and have a few bits of advice to share, but I'm always welcome to here any tips, tricks, or strategies anyone else comes up with! Please comment any below.


-This is a challenging play style and is not one I recommend for beginners. Depending on RNG and your actions, you could easily see yourself at war with the majority of the world before you've had any time to build up. The USA's starting situation leaves a lot to be desired, with an underequipped army and a lackluster war industry.

-The HDEA doesn't seem to clear the Great Depression if it's not at full capacity. i.e taking focuses like the Agricultural Adjustment Act will reduce the penalty like normal, but won't allow you to clear it instantly

-Get your army, navy, and air force organized before they declare war on you. If you're planning on doing any naval invasions, make sure they're ready to launch the moment the war kicks off. If you're worried about your northern border, have troops stationed there before the UK can call in Canada. Take note of all their holdings before you go to war, they have many small islands which can boost their naval range to your front door.

-France will join the Allies historically, but I'm not sure if doing this strategy impacts the timeline at all. In my experience, they still seem to join around mid-late 1937, meaning you don't have too much time to focus on knocking out the French navy before the Royal Navy gets involved too.

-Screen your convoys, Japan, the UK, and France have subs and close naval ports, expect the entire east coast to be swarmed by wolfpacks.


Japan:
I've managed to knock out Japan before they've gone to war with China, but it requires lots of prep, luck, and min-maxxing. Abandon the Atlantic and most of your army, reduce yourself to ~a dozen divisions and just focus on blitzing your way across the Pacific. Build up your army as much as you can, as quickly as you can. Take islands close to Japan and try to land and encircle a few division on the mainland of Japan. Japan doesn't have a huge industry and the majority of its land forces should still be squatting next to China. Stack submarines around the Home Islands to prevent them from getting oil or moving troops. After you make your initial landing, they should station most of their remaining troops on your front line. If you have trouble pushing through, just make landings along the remaining coast of Japan, virtually all of their victory points are within range of naval invasions. Don't forget to use your navy for shore bombardment bonuses, even on non-invasion battles.

France:
Annoying to reach and has many close ports, but can be dealt with quickly if you focus your forces correctly. If you stack your navy correctly you can easily cripple theirs in just a handful of engagements while using submarines to cut off their supplies in the Atlantic. Naval hop around the Caribbean, invade into French Guiana, cross the pond into French Africa, invade into North Africa, then finally attack mainland France. They'll still have the Disjointed Government surrender debuff, so if you reach Paris they'll fold.

UK: Even more annoying to reach, also has close ports, and brings in its domains to the fight. Has the strongest navy and an annoying advantage at defending. (RADAR, AA, strong airforce, longer naval distances, etc.)
Knock out Canada ASAP, and basically just follow the French plan above but with extra steps. Take out any British land along the way and try and snake your way up to the English Channel. The US Navy is strong but not perfect. Remember to provide air cover and to repair your fleet ASAP. Optionally, dedicate a few dockyards to subs/cheap destroyers with mines to help cover your approach. Saturate the area around Great Britain with mines and use subs to cut off their convoys. They're also fairly dependent on the import of oil, rubber, and other strategic resources. Depending on world affairs, taking out the UK should also end the war and let you take over the rest of the Allies.