I'd like to get navals back in a balanced and funny reward doc, so here's a suggestion.
(Really hope it's easy to create cos maybe only 1 new icon effect needed when navals hidden behind green cover. When sniper shot them - smth existing can be used for sure.)
LEFT hand doctrine "naval manpower":
[2cp] Navals. 5 men call-in. Armor between RBS strelky / guards and common strelky, closer to strelky of course. (Won't be upgraded along with RBS upgrade.) Movement speed slightly less than strelky.
Cost 310 (no RBS bonus, no ability to build defences or outposts due to better armor on them and ammo reserved for close combat; if OP then just make ordering them longer), specialize in close combat (strelky-strafniki rifles for everyone from the start? or just 3 of them?) so can get 3-4 PPS-43 (worse than RBS ppsh) or 1-2 dp-28. They can still pick up some ptrs or enemy shreck though.
When in green (not yellow!) cover, get the best def bonus. Even vs grenades (not flamers!). But also about 50-70% offence decrease. Kinda hide bodies behind cover so well, that it's hard to shoot! It can be done by changing reload speed to be replicated visually. That's how they used to hide on a ship. Reasonable to ask for an icon or a symbol of a man hiding his head or alike.
1) they hate snipers so much, that every (squad member's? or just ally close by?) death from a sniper gives them anti-suppression and speed bonus for 15-20 secs (could ask for some icon and effect here?). Additional damage to snipers in close and mid range always.
2) they have normal grenades from the start. + they can use 3-4 non-sticky (!) instablowup (!) grens tied together (or a satchel charge if hard to implement) for about 60-80muni for building or bunker destructon plus to chase away or temporarily immobilise \ harm enemy tanks, if they didn't drive away.
3) They carry a lot of grens and own armor so no ability to build defences or outposts (maybe even can't cap points). But can purchase minesweeper (takes 1 weapon slot, what decreases firepower a bit) or maybe even cut wire - they expected territory to be guarded, when arrived.
4) They can break suppression for a cost of 1-men death! Like, open rush to enemy mg or a bunker led to a casualty due to kinda self-sacrifice.
+ they reinforce slightly faster than strelky, but not as fast as conscripts
+ at least here soviet major should get 5-th member, i.e. bodyguard! Or just 5 navals close to him instead.
[2cp] "Naval Training" - this doc should buff weapon teams health 15-20% and turn speed.
+10-15% faster reload for mortar (maybe only for usual one, whatever)
10-15% faster reload for AT - no great tank bonus here, no zis-2, so at least overall weapon teams bonus to rely on their training
+ 4 men crew for AT guns instead of 3 - never ever anywhere implemented, so will be fun! to be more res vs sniper spam
+ maybe deployed medical truck gets 20%more health
+ soviets once had "mechanics" unit with fast repair! we can buff repairs here?
[2cp] "Naval Reinforcement" (lowest button in doctrine hand) - if all armor is destroyed lategame, player can call-in T-34-85 + stsappers + AT (with "post-payment" or what's better - just cheaply; 5 sec delay between every unit appearance). (Kind of analogue what I suggested for ostheer to be more resistant lategame for not to wait until base destruction.)
(possibly most problematic point and can be replaced by smth - like simply call those stsappers from battleship)
RIGHT hand doctrine "battleship support":
[1-2cp] naval reserves?
+ mines for 20 muni "from battleship reserve", but only for common weak engies, coz no great tank bonus here, no FLAK etc.
+ allow common engies to place AT mines "from battleship reserve" like partisans did (after "men against tanks" upgrade)
+ common engies 15% faster repair speed tnx to more details available and tools from battleship (like ostheer elite reward doc should provide the same)
+ provide buyable KV-1 for a reasonable price (390-400mp?), that can give surrounding infantry yellow cover as a mobile fortress? (or some unused tank model for fun). ships brought in some old reserves kinda. It will be fun coz not as fragile as T-34 and can crush \ soak mines!
[2cp] Naval doc could use some help from a remote ships like "3 fast gunshots" for about 90 muni: only 3 arty hits will get in a rather close area relatively fast (even call-in is fast like 3 secs, without effects for an anemy) to destroy bunkers or buildings or tank blobs. Fastest to react but somewhat weakest arty!
+ [2cp] (lowest button in doctrine hand) possibly price cut for t-34 as a last point in some tree (like prop already does, but only for t-34). Or is-2, or SU, not sure: the idea is to cheapen certain tank like prop doc does, but additional details were provided only for some technique.
another option could be increase some soviet tank (like SU? new engies for SU?) speed 10% due to naval engine rework (this never existed in any doc), but this is mostly for fun. (The point was again to diversify soviet player from is-2 rush all the time, providing costly but powerful su100 instead more health and damage for a really costly upgrade.) here soviet lack powerful penetration guns, so maybe only SU's should be faster and cheaper.