This is a 民族精神 of Japan in the 
Waking the Tiger DLC. The spirit starts as "balanced" but can be affected by the Interservice Rivalry (IR) decisions.
The decisions are comprised of four pairs of mutually exclusive decisions, with any pair offering to either favour the navy or the army, giving a national spirit for the decision and changing the balance of the Interservice Rivalry national spirit.
National Spirit Mechanics
The national spirit uses a 5 step scale of Army dominant to Navy Dominant. While a balanced rivalry has no effect, strengthening either branch of service results in modifiers to factory output and construction speed with "branch strengthened" and further modifiers to research and planning speed with "branch dominant".
| Interservice Rivalry Status | Dockyard/ Factory Output |
Dockyard/ Factory Construction Speed |
Other effects |
|---|---|---|---|
 Army dominant
|
-20%/+10% | -20%/+10% | Land doctrine research speed +5% Naval doctrine research speed -10% Naval research speed -10% |
 Army strengthened
|
-10%/+5% | -10%/+5% | - |
| Balanced
|
- | - | - |
 Navy strengthened
|
+5%/-5% | +10%/-10% | - |
 Navy dominant
|
+10%/-5% | +20%/-20% | Naval doctrine research speed +5% Planning speed -10% Land doctrince research speed -10% |
Decisions
Each decision is mutually exclusive with its counterpart, so the effects are mutually exclusive as well. It costs 50 
PP to take a decision and after each decision comes a 180 day cooldown before the next one can be taken. However, there is no strict order in which any decision can be taken.
Furthermore, a decision taken affects the Interservice Rivalry national spirit, taking it one step towards the last choice. So, a "balanced" rivalry becomes "army strengthened" after the first pro army choice and becomes "balanced" again when choosing the navy next.
Prioritize Steel for Guns - get +2 
MIC in 2 random states
Prioritize Steel for Guns - get +2 
NIC in 2 random states
Prioritize Army Aircraft Construction - -10% 
production cost for CAS and tactical bombers
Prioritize Navy Aircraft Construction - -20% production cost for carrier fighters, carrier CAS, carrier naval bombers and naval bombers
Institute Indiscriminate Conscription - +2% 
recruitable population
Grant Draft Exemptions - +5% MIC and dockyard output
Form Raiding Regiments - +5% attack and defense for special forces
Form Special Air Landing Forces - +2% special forces multiplier
Strategy
The Interservice Rivalry (IR) national spirit functions very similarly to a focus tree branch and should be considered as one for the japanese build up. While individual decisions and their respective bonuses must be considered, the IR national spirit and its effects also do play a role. If engaging in a landlocked conflict early on, like against China or the Soviet Union, it is advantageous for Japan to first choose an army favouring decision(s). This gives both the national spirit bonus for the decision itself as well as the added bonus from army strengthened or army dominant national spirit. As in the later game, Japan will almost inevitably confront the allies, it needs to favour the navy in later decisions. A "navy strengthened" or "dominant" national spirit can give Japan an edge in the naval buildup between 1938 and 1942 before confronting the Royal Navy and the US navy. Since not all IR decisions are created equal in terms of the benefits they offer, especially given their interaction with Japan's national focuses, they can be discussed as follows:
Pritoritize Steel for Army/Navy: very much comparable in terms of the benefits. Depending on Japans buildup strategy, either one makes sense. With the early war against China or the SU looming, steel for guns comes out slightly on top.
Prioritize Army/Navy Aircraft construction: hands down, navy is the winner here. The reason for this is that CV aircraft are actually cheaper than their land based coutnerparts, the bonus affects more types of aircraft, all of which are vital to Japan. The final reason being the Zero NF and Mitsubishi designer. Combining the designer, the 1940 fighter NF and this national spirit makes the IJN air arm a force to be reckoned with.
Indiscriminate Conscription/Draft exemptions: Recruitable population can become an issue as japanese land forces tend to cover extensive territories. However, this can be mitigated by using colonial troops after pupetting China. The factory output increase through draft exemptions benefits both branches of service and, together with the existing game mechanics' substitutes for recruitable population increase, makes it come out on top.
Raiding Regiments/Air Landing forces: Despite Japan getting an increase of special forces by national focus already, the meagre +5% attack/defense increase for special forces does not look appealing in comparion. This can be chosen either way, but the favour navy decision looks better.