The most important information you can have is what information the enemy has about you.
The Military doesn't spend money for fun.
A good example is tank gun ammo. There is no prize for having the most powerful tank ammo. Developing ammo and deploying it costs money so your ammo is generally designed to penetrate your primary enemies tank frontal armour from 2,000m most of the time.
The job of the people building your tank is to make sure that your tanks frontal armour will stop the enemies best tank round and most of his missiles within reason.
The US will not bother to develop armour for the Abrams that will stop the 317kg shaped charge warhead of the Kh-29 family of medium missiles because no level of mobile armour will help... these missiles are designed to undermine the concrete foundations of bridges and other heavy structures so no level of tank armour will be good enough.
The point is that if the US had never learned about the performance of several ERAs the Soviets and Russians have developed they would not have developed the higher penetration rounds that they have because there would have been no requirement.
Equally the Russians, if they had money during the 1990s would have already had longer rod penetrators in service as they were needed. They have developed a larger calibre gun to allow for future armour protection increases in western tanks but have decided there is room for further growth with 125mm rounds that will make it effective for the foreseeable future.
Improving ammo is not cheap... it is actually quite expensive and includes production of enough rounds to get it into service in significant numbers to make the cost worth it, but it is still cheaper than introducing a new calibre.
A new larger calibre would make guided rounds and HEAT rounds more effective.
In other words what I am saying if the Russians can detect and track new US subs it is not in their interests for the US to know that because it might be some trick they are using that could easily be defeated.
I remember one time reading about a western force that transmitted IFF signals to enemy aircraft back when IFF systems were new. They could use the IFF responses to detect the aircraft type and location without using radar. IFF systems got more sophisticated and only started responding to specific signals... but you see what I mean about sneaky tricks?