History of the introduction of the actual G40 OOB Subs rules

[baron Münchhausen]

As I was working out this House Rule with Subs, TacBs and Fgs, I realized that there was no absolute reason for this complex rules about planes needing DD to hit any subs. The actual Subs surprise phase creates by itself the need of DD to forbid subs to submerge before the planes attack in a SZ.
So why add this layer of complexity?
Is it because of the extreme attrition amongst submarines or the unpopularity of the unit, or something else?

Does anyone know when it appears (amongst A&A games) for the first time, and if there is some other intermediary steps between classic Subs, the Iron Blitz subs with DDs, and the actual one (I made the jump from MB classic to Spring 1942)?
And do you have any hint about what made the change a compelling one?

I put below the line of reasoning which makes me realized I have no real clue about the origins and assumptions behind the actual OOB subs rules.
It is not intended to discuss this HR, there is already a thread where you can post any comment, but to help me understand the evolution of subs rules (and of destroyers ASW, I suppose).
Thanks for sharing you understanding and experience.

@Baron:

@Baron:

Do you think this last HR makes Carriers too much vulnerable against Subs if they put 1 Fg and 1 TcB on board?

Does this cutting in half the defensive power of Carriers against Subs should be balance by a no restriction against Subs for Tactical Bombers?

TcB A3-4D4M4C10 can hit Subs anytime by themselves. No need of Destroyers.

But StB units (any number) can only hit submarine units when paired to at least 1 destroyer unit.

Who knows? Some ideas to judge this situation?

Don’t you think it could help simplify the Rules on the subs vs aircrafts?

Because, there is only StBs needing DDs on offence which can be part of any naval combat with Subs ?

Actually, this line of thinking pushed me further away.

Once fighters can no more hit any Subs, I thought why not simply allows both TcB and StB to hit subs without the need of destroyers.
But, at the same time, keeping all the actual stuff on DD and subs.
That would meant that any type of bombers attacking subs only in a given SZ should not be able to do any harm to them since subs keep their Surprise phase and can submerge prior to the regular combat phase. In other terms, DDs will still be needed on many circumstances to get a chance to hit subs.
So with Fg unable to hit them and the Subs submerge still very efficient, giving Bombers the ability to hit subs will not doom them.

That’s how I see things, am I under a false impression?
Do you think it is playable?
Because, it could be much simpler to play subs vs planes than the actual OOB.
Hope you can leave a comment.
Thanks.

Edit: A long time ago someone thought about the same amendment to the regular OOB Subs rule:
http://www.axisandallies.org/forums/index.php?topic=13689.msg395215#msg395215

[baron Münchhausen]

@ShadowHAwk:

Well it makes the game more balanced.
Sure air units can attack a sub, but a sub can also attack airunits most had AA guns.

So just to keep things simple air cannot attack a sub without a DD present. Its a game not a simulation so lets keep it playable.

Thanks for your answer ShadowHawk.

I know this game isn’t the most accurate simulation, and wasn’t intended to be.
My interrogation is upon these 2 points:
why does it make it more playable (from my POV, it is the contrary: an additional layer of rules and a complexity of situations to make someone puzzled)?
and how does it really improve the game balance?

I think I just found the breaking point in OOB Subs rules:
From 50th Anniversary Edition, to Global 1940 1st edition.

In Anniversary Edition, p. 30, the subs vs planes are mentioned only in the Subs Units Profiles:

Submersible: Anytime a submarine would otherwise roll the die to attack or defend, it can submerge instead. This removes it from the combat it can no longer attack or take hits in that combat. Whenever a round of combat starts and a submarine is in combat with only aircraft, it can submerge (before aircraft fire).

I also read this on the Destroyers profile Anti-Sub Vessel section, p. 29:

Anti-sub Vessel: If a destroyer is in the same space as one or more enemy submarines, it cancels the Submersible, Surprise Strike, and Sub Movement special powers of those submarines (but not any powers gained through research & development).
Additionally, your aircraft may attack enemy submarines.

The last addition seems like a side note as the consequence of cancelling Submersible power of the subs.

In Europe 40, 1st Edition, p. 30, here is the rule on planes vs subs found also in the Subs Units Profiles:

Can’t Be Hit by Air Units: When attacking or defending, hits scored by air units can’t be assigned to submarines unless there is a destroyer that is friendly to the air units in the battle.

And at p.29 on Destroyers profile Anti-Sub Vessel section, we can read this:

If a destroyer is in a battle, it cancels the following unit characteristics of all enemy submarines in that battle: Surprise Strike, Submersible, and Can’t Be Hit by Air Units. Note that destroyers belonging to a power friendly to the attacker that happen to be in the same sea zone as the battle don’t actually participate in it, therefore they don’t cancel any of these abilities of defending submarines.

So, somewhere in the history of the Subs OOB rules, the submerge ability was seen as a balance one. But then, it gets in complexity, so in certain situation defender is not be able to use subs as fodders because there is no enemy’s destroyer.

But, in Anniversary, planes were able to hit subs, so a defender could use subs as a fodder.

Another question rise:
this addition about planes needing to be paired with DDs, was it because Subs were too good and a wonderful fodder (at 6 IPCs) to protect warships (instead of DDs)?
Or because Subs were still too vulnerable (I can’t see how, help!!!) against planes and was too easy to destroy a whole fleet by air only?
(If the defender was too dumb to forget to submerge all the subs?)

In this last option, maybe a lot of planes can get an overkill of costlier warships but cheap subs may still survive. But the contrary is not possible.

I just imagine 10 planes making 6 hits against 3 warships and 3 subs. Here the 3 subs are saved, and 4 additional hits are an overkiller and lost somehow for the attacker.

[baron Münchhausen]

@ShadowHAwk:

Well it makes the game more balanced.
Sure airunits can attack a sub, but a sub can also attack airunits most had AA guns.

Guess there will be loads of other variables not mentioned here.

So just to keep things simple air cannot attack a sub without a DD present. Its a game not a simulation so lets keep it playable.

Historically (from what I can understand of it), the Flak batteries of Subs were almost as inefficient as the machine guns of StB. It works on rare occasion, but at the strategical level of A&A, it is not relevant.
Edit note:
Here is a summary of the casualties due to U-boat’s AA flak:

The risks in combat with the Axis submarine forces were not totally in favor of the Allies. As the war progressed, German submarines in particular became more heavily armed with antiaircraft defenses. At least 57 U.S. aircraft were shot down by U-boats compared to only 12 U-boats lost in these attacks. The RAF Coastal Command alone lost 700 aircraft that were badly damaged, shot down or written off after encounters with U-boats.
http://www.history.navy.mil/avh-vol2/Appen3.pdf

I ever read that at a certain time the war (1942 or 1943?), U-boat commander receive the order to stay on surface and fight the planes (mostly Tactical Bombers and Fighters working together). They shortly realized it was not a good idea and were too much an easy target for aircrafts.

U-271 was one of seven U-boats converted into U-flak boats to serve as surface escorts for the incoming/outgoing attack U-boats operating from the French Atlantic bases. They had greatly increased antiaircraft firepower and were intended as aircraft traps by luring Allied aircraft to attack these heavily armed U-boats. The converted boats proved effective for little more than two months before the Allies developed countermeasures. U-271 operated briefly as a U-flak during October 1943, providing AA cover in the refuelling area north of the Azores. All U-flaks were converted back to attack boat configuration in November 1943. It should be noted that by late 1943 the U-flaks had become redundant due to improvements in the standard AA armament for U-boats.

That’s why we can agree that this Subs incapacity:

Can’t Hit Air Units: When attacking or defending, submarines can’t hit air units.

is quite historical.
And from my perspective, is the most simple way to be a simulation of what happen about the anti-air capacity of Subs.

EDIT: But at the same time, we can easily consider that each single Sub with AA Flak were much more dangerous in itself against 1 single fighter.
In addition, as said elsewhere, (as far as I know of) no lonely fighter was able to sink down a submarine.
Taking into account these two historical aspects, the rule on Fighter should be as restrictive as it is for Submarines (since U-boat have a better killing ratio of F4F Wildcat than the reverse).
No plane can hit subs.
On the contrary, TcB (Avenger) and StB (B-24 Liberator) should be able to hit Subs directly.

[baron Münchhausen]

@ShadowHAwk:

And for unescorted carriers doesnt it sound strange that the Airunits are in the air for a surprise strike.
How would that work, well guys we are going to be attacked in a moment so just get in the air and act surprised.
Not counting the fact that sailing a straight course to launch the fighters would be suicide.

And once you are hit by the surprise strike you cant launch the fighters unless you want to give the sub a clear 2nd shot, and the damage would most likely prevent flight operations anyway.

So to make it realistic if a carrier gets attacked by only subs and it does not have DD escorts the airunits will not be in the air defending.
But if it does have a DD present then the air units are in the air. But if there are more subs then DD’s 1 sub gets a guaranteed shot at the carrier because it makes itself completely unable to dodge while launching fighters.
Guess there will be loads of other variables not mentioned here.

Your example can be good at an individual level like it was the story of the first UK escort carrier HMS Audacity, caught off guard at night and without enough destroyer escort:

As Audacity left the convoy on the night of 21 December,[10] one of the merchantmen fired a “snowflake” flare which revealed her in silhouette to the German U-boats. The submarines had been given specific orders to sink her as she had caused a lot of trouble for the Germans both at sea and in the air.[3] The first torpedo fired by U-751 under Kapit�nleutnant Gerhard Bigalk[9] hit her in the engine room and she began to settle by the stern. The next two torpedoes caused an explosion of the aviation fuel[11] blowing off her bow. Audacity sank some 500 mi (430 nmi; 800 km) west of Cape Finisterre at 43�45′N 19�54′W.[3] She sank in 70 minutes. Her survivors were picked up by the corvettes Convolvulus, Marigold and Penstemon,[12] one of the survivors being pilot Eric Brown.[13] German propaganda claimed that Audacity was a 23,000 long tons (23,000 t) Illustrious-class aircraft carrier, rather than an ex-merchant ship of less than 6,000 long tons (6,100 t).[14]

Part of the reason for her short life was her placement with respect to the convoy. Escort carriers could either sail within the convoy, giving them the protection of the convoy’s escort vessels, but at the cost of limiting the manoeuvring space which is required to turn the carrier into the wind to operate aircraft, or they could operate outside the convoy. Operating in the area near the convoy gave the carrier all the space it needed to turn as required for aircraft operations but necessitated a second escort for the carrier alone. The carrier could also prove a target for the convoy’s attackers, leading them to target it first, to which the answer would be to operate at some distance from the convoy. Audacity had been operating outside the convoy, a procedure that was later prohibited by the Admiralty as too risky

http://en.wikipedia.org/wiki/HMS_Audacity_(D10)

But Axis and Allies units represent many Carriers (from 4 to 8 fleet carriers) and planes.
It is at least a 4 month turns also.
So, at this strategical level, it is easy to assume that when a few carriers were damaged, planes could have fly elsewhere, where already on a mission, or something else.

It is the same perspective from Subs POV, the “hit” could represent many skirmishes of many subs against some carriers. No only a single torpedo run.

It is an highly abstract level, in which any rules apply to an average but representative situation.
Clearly not an exception at an individual level.

[baron Münchhausen]

@ShadowHAwk:

Well it makes the game more balanced.
Sure airunits can attack a sub, but a sub can also attack airunits most had AA guns.

So just to keep things simple air cannot attack a sub without a DD present.
Its a game not a simulation so lets keep it playable.

As a matter of fact, fighters (F4F Wildcat were put on escort carrier) can attack subs but doesn’t seems able to sink them by itself, needing his big brother the Avenger torpedo-bomber (a kind of TcB) or the help of Destroyers to finish them off. Here an historical example:

On 17 December U-131 was spotted by a Martlet aircraft from the escort carrier HMS Audacity while shadowing Convoy HG 76 as part of the Seer�uber (English: “Pirate”, lit. “Sea Robber”) wolfpack.[5]

U-131 was forced to dive, while ships of the 36th Escort Group, commanded by Frederic John Walker in HMS Stork, with four other escorts; such as the destroyers HMS Exmoor, Blankney and Stanley and the corvette Pentstemon, approached to continue the attack. Detected by Stanley’s ASDIC (sonar), she was depth charged by Pentstemon, and forced to surface, due to chlorine gas coming from the batteries. Unable to dive, she attempted to escape by running at full speed on the surface. While under pursuit U-131 shot down an attacking Martlet aircraft, killing the pilot, but was then shelled by the escort group, which scored several hits. Realizing that the situation was hopeless, the crew abandoned the U-boat and scuttled her. All 47 of the crew survived and were taken prisoner.

http://en.wikipedia.org/wiki/German_submarine_U-131_(1941)

So, in a G40 with TcB, you could have easily represent this way of doing subwarfare by instating this rule (instead of the OOB planes need DD):

A fighter unit can never hit sub unit.
When paired 1:1 to 1 DD A2D2 or 1 TcB A3D3,
Fighter unit gives this destroyer/Tcb unit +1 A/D, when there is at least 1 enemy’s sub.

So you can still apply some kind of aircraft pairing rule bonus with DD, while at the same time better show the role of Fighter plane (as a scouting air patrol unit in ASW) during the war.

That is another direction to develop subs rules while reducing the impact of aircrafts on submarines.

The developer didn’t choose this way. Maybe it wasn’t there intention.

Clearly it was for a reason.

Why did they add this layer of complexity about Subs cannot be hit by aircraft without DD?

Better for lowering Subs casualties?
Better incentive to buy Destroyers?
Helping mostly planes only attackers on warships, by making impossible the use of Subs fodder?

Other hypothesis?
Please, help me understand this transition in the subs rules, from Anniversary to Global.

[baron Münchhausen]

Here is the beginning of an answer from the developer perspective.
It explains the reasoning behind the last OOB Subs rules of Spring 1942, so it applies also for G40 1st and 2nd editions.
I bolded the most on the topics aspects:
@Krieghund:

Planes were very effective sub killers in reality.  However, reality suffers a bit when translated into an abstract board game.  Sometimes the designers have to “fudge” one aspect of a reality-based game in order to deal with the limitations of another aspect of it.  Hopefully, in the end, the two balance each other out to create a whole that abstractly mirrors reality even though the individual parts may not.  The interaction between subs, destroyers and planes is a perfect example of this.

The range of air units and the size of the oceans in the game make it very easy for air units to find and eliminate subs, if air units are capable of hitting them on their own. This gives subs no place to hide and makes them “sitting ducks” for air attacks, as was demonstrated in the Revised edition. This simply doesn’t reflect the realities of anti-submarine warfare as it occurred in World War II, at least until long-range aircraft were developed later in the war.  Until that time, subs were very safe in the middle areas of the oceans, as planes didn’t have the range to hunt them effectively there.  Most were sunk only when they were caught in the act of raiding shipping.

Adding the rule that destroyers are required as “spotters” for air attacks against subs represents the concerted effort needed to hunt and attack subs hiding out between raids.  This gives subs more longevity and makes them more the fearsome foes that they actually were in the early to middle days of the war.

It also promotes the purchase and maintenance of more well-rounded fleets, as destroyers are necessary to guard against the threat of subs.  This reflects the reality that subs were a constant threat to military shipping as well, and that no convoy would travel without destroyer escorts because of that threat.  At the same time, it keeps them from being used as cheap “cannon fodder” in naval battles, as they were most often not used extensively in fleet operations, but rather as harassing hunters where their unique properties were best utilized.

From an economic standpoint, the necessity of buying destroyers for protection against subs also reflects the economic losses sustained by raids against merchant shipping by submarines.

All of these points, taken together, allow the game to abstractly represent the economic and military threat posed by submarines in World War II.  This makes subs a useful and strategic purchase in the game.  I hope this sufficiently answers your concerns.

[baron Münchhausen]

@Krieghund:

Planes were very effective sub killers in reality.  However, reality suffers a bit when translated into an abstract board game.
 
Adding the rule that destroyers are required as “spotters” for air attacks against subs represents the concerted effort needed to hunt and attack subs hiding out between raids.  This gives subs more longevity and makes them more the fearsome foes that they actually were in the early to middle days of the war.

It also promotes the purchase and maintenance of more well-rounded fleets, as destroyers are necessary to guard against the threat of subs.  This reflects the reality that subs were a constant threat to military shipping as well, and that no convoy would travel without destroyer escorts because of that threat.  At the same time, it keeps them from being used as cheap “cannon fodder” in naval battles, as they were most often not used extensively in fleet operations, but rather as harassing hunters where their unique properties were best utilized.

All of these points, taken together, allow the game to abstractly represent the economic and military threat posed by submarines in World War II.  This makes subs a useful and strategic purchase in the game.  I hope this sufficiently answers your concerns.

As far as I understand, the main reason for adding the “planes needs DD spotter to hit subs” is coming from an historical accuracy argument on fleet distribution and about the role of submarine as “harassing hunter”.

So, it means that in Anniversary, the Subs were used extensively as cannon fodder to protect fleet.
And they decided to change it. Am I right?

Is it different in OOB Sub rules in G40? Subs can’t be used as much as fodder?

EDIT: So, it means that in REVISED, the Subs were used extensively as cannon fodder to protect fleet. And they decided to change it.

[baron Münchhausen]

Here is the first step to help me better understand the chronology and evolution of the Subs rules:
@Krieghund:

Air units can hit subs in Revised without a friendly destroyer being present. This requirement from AAE and AAP was dropped in Revised in the interest of simplifying unit interaction.  It was reintroduced in AA50, as removing it made subs too fragile.

As far as I understand now, there was 3 sets of Subs rules:
1- Classic:
Can submerge at the end of the first round. And can be hit by air. (no DD unit existed.)

2- AAEur and AAPac:
Subs can submerge during First Strike phase and cannot be hit by aircraft. (Planes need DD.)

3- Revised:
Subs can submerge during First Strike phase but can be hit by planes. (DD still needed to block submerge.)
EDIT: My mistakes: subs can only submerge after regular combat phase.

4-AA50 returned to #2 (It is clear, once you read the FAQ and Errata).

5-G40 1 st, 1942.1, 1942.2, G40 2nd ed., same as #4 and #2.

---

So #3, proved that under Revised the Subs rules were simpler.

But it left to know what Krieghund mean by “too fragile”…
Do you have any idea?
Hope he will provide us some details…

EDIT: Probably miss a subtle difference according to this:
@Krieghund:

@Gargantua:

The submarine had to (survive) a combat before submerging.

In Classic 3rd edition (defending only, no subs can submerge in Classic 1st and 2nd editions) and Revised, yes.  In original Europe and Pacific, attacking subs can submerge immediately, while defending subs must survive attacking fire first.

[baron Münchhausen]

Here is a comment and his reply which I still found pertinent, even if written a long time ago:
When the Subs rules change from the simpler one from Revised to the other AA50:
@Black_Elk:

I think submarines are causing way more confusion to rules/gameplay then they are worth.

My first reaction to the new rule, is that it just seems to make submarines an even more marginal unit than they were before. The inability to take hits on submarines that are part of a fleet (from attacking enemy air), makes airpower even more significant than it was in Revised, since now you can just trade fighters for capital ships.

For submarines to be relevant to the gameplay, they should really be designed to inflict economic damage. As a combat unit they’re pretty underwhelming.

@Romulus:

From an tactic point of view this rule is better, if we consider it together with the new transport status.
Surface fleets and submarines did not operate togheter during ww2. So having the sub (and the TRNs) as cannon fodder for surface battle is not historically correct, is not tactically correct and even from a gaming point of view it hampered war on the seas.

In this game the real backbone of the fleet is the DD, that should be built in good numbers.

It is true that a fleet with AC and submarines as cannon fodder could suffer grievous losses to air power… but also a fleet with a lone DD if attacked by a bunch of subs (that cost 6 i.e 4 IPC less than a fighter) could be wiped away leaving fighters (immune to subs fire…) to look for a place for landing.

So I agree that it is possible to use air power for trading with capital ships (right what happens in the real war, the aircraft pilots are trained to attack valuable target not useless TRN or SUBS… imagine the battle of Midway and USA Dauntless pilots sunking four submarine instead of four AC…) but also subs may be used for trading with any kind of target that is not an aircraft, i.e. DD, CA, AC and BB. I see a paper-scissors-stone pattern in that.

@Romulus:

I think that allowing the aircrfats to sunk sub without retaliation from the subs makes the subs completely useless as “sub” but useful only as “naval cannon fodder” and relegates the DD to a secondary role.

In our f2f revised games a tipical fleet is composed of x BBs, y ACs, 2 * y FIGs, n TRNs, m SUBs, 1 DD (the flag ship?). Only time in which I see more of one DD it is when someone developed combined bombardment. I usually play without technology so go figure how many DD we use in our games.

According to me, with anniversary rules we are going to see two “historical” behaviour:

• DD have to be bought in larger quantity because TRNs and SUBs are not useful as cannon fodder;
• DD have to be used to hunt SUBs.

This means that we are going to see fleets more similar to the real WW2 counterpart: few Capital Ships escorted by a lot of DD. (Usually a good DD screen for Capital ships involve 3-2 DD for each Capital ship). Moreover subs should operate alone or in groups of subs, and who want to use the sea as a way to transport land units have to fight against subs.

I know that historically aircraft where used against subs, but also DD where used in great quantity for patrolling the seazones and for escorting convoys.
Moreover they were dedicated aircrafts, as said in the quote on ASW Tactics you proposed.
The dive bomber and torpedo bomber on the Attack Carriers of the USA Pacific Fleet were not intended for sub hunting.
Escort Carriers were equipped with aircrafts used for patrolling and for attacking sub.
Furhtermore the aircrafts were useful to force the subs to stay submerged. A submerged sub, in fact, is completely safe from air attack, only a DD equipped with depth charges may try to hunt a submerged sub.

For example the USS Cavalla, a Gato class submarine, sunk a Japanese Fleet Carrier in the Battle of The Filippine Sea, in the face of aircrafts and DDs of the Japanese Combined Fleet.

On her maiden patrol Cavalla, en route to her station in the eastern Philippines, made contact with a large Japanese task force 17 June. Cavalla tracked the force for several hours, relaying information which contributed to the United States victory in the Battle of the Philippine Sea (the famous “Marianas Turkey Shoot”) on 19 � 20 June 1944. On 19 June she caught the carrier Shōkaku recovering planes, and quickly fired a spread of six torpedoes for three hits, enough to sink Shōkaku at 11�50′N 137�57′E / 11.833, 137.95. After a severe depth charging by three destroyers, Cavalla escaped to continue her patrol. The feat earned her a Presidential Unit Citation.

(Quote taken from: http://en.wikipedia.org/wiki/USS_Cavalla_(SS-244))

Also in the Mediterranean German U-73 managed to sunk the UK Aircraft Carrier Eagle, 11th of August 1942.

(http://www.uboat.net/allies/warships/ship/3255.html)

@Romulus:

@Imperious:

According to me, with anniversary rules we are going to see two “historical” behaviour:

• DD have to be bought in larger quantity because TRNs and SUBs are not useful as cannon fodder;
• DD have to be used to hunt SUBs.

Destroyers are the Infantry of the seas. not subs. That was a mistake in Revised and now its corrected.

I agree with you IL. I am very happy of this new course for A&A sea war!

@Cmdr:

I think we need to think more about this.

If the submarines are attacking your carrier, then you KNOW where they are.  Just follow the torpedo contrails!
The reason fighters couldn’t just go out and attack submarines is because the submarines are not firing torpedoes to use to track them down.  Thus, you need destroyers to FIND them. (Although, I submit bombers should be able to fill this role as well, possibly with the caveat of having heavy bombers.  After all, America at least, and I’m kinda sure England too, used bombers with sonar buoys to find enemy submarines too.)

[baron Münchhausen]

@ShadowHAwk:

@Baron:

But Axis and Allies units represent many Carriers (from 4 to 8 fleet carriers) and planes.
It is at least a 4 month turns also.
So, at this strategical level, it is easy to assume that when a few carriers were damaged, planes could have fly elsewhere, where already on a mission, or something else.

It is the same perspective from Subs POV, the “hit” could represent many skirmishes of many subs against some carriers. No only a single torpedo run.

It is an highly abstract level, in which any rules apply to an average but representative situation.
Clearly not an exception at an individual level.

If you look at the layout at the start of the game the capital ships are basicaly just 1 or 2 of the type not more.
But that being said if a carrier would be a carrier group from WW2 then a sub even a group of them would never get close because of the destroyer screen.

There have been very little cases of a battleship or a carrier sailing without some destroyer escort.
Also transports would not really be defenseless if they would have escorts build in, most subs where put off attacking a transport fleet because of the escorts.

If you would have to model all these things into the game you would need a lot more variables and rules for subs. Also fleets with subs would become much more powerfull and subs alone would be just as weak as they are now. 1 destoyer + 10 fighters vs 5 subs is always a good result for the attacker.

I let you read about this Japanese Carrier, it tells us how the Fog of war is so unpredictable:

Shinano (信濃?), named after the old province of Shinano, was an aircraft carrier built by the Imperial Japanese Navy (IJN) during World War II. Initially laid down as the third of the Yamato-class battleships, Shinano’s partially complete hull was converted to a supercarrier in 1942, midway through construction. Over the next two years, the ship was heavily modified and she became the largest aircraft carrier built up to that time.

Partially completed in November 1944, Shinano was sent from the Yokosuka Naval Arsenal to Kure Naval Base to complete fitting out and transfer a load of 50 Yokosuka MXY7 Ohka rocket-propelled kamikaze flying bombs. En route to Kure, she was sunk on 19 November 1944, 10 days after commissioning, by four torpedoes from the American submarine Archer-Fish. The ship carried an inexperienced crew, had serious design and construction flaws, and was not ready for combat. Over a thousand of her crew and passengers were rescued, but 1,435 sailors and civilians died, including her captain. Shinano remains the largest warship ever sunk by a submarine.

And this super carrier have 3 Destroyers for close protection…
So, with such a case, it can be possible to translate this in A&A such as 1 sub unit giving 1 hit against an undefended CV unit.
Don’t you think?

And there is also the story of the Musashi, which can probably be 1 single BB unit by itself. So 1 single submarine (clearly not 1 sub unit) was able to damaged it enough that she needs repair (which can be seen as a damaged BB by sub):

Musashi (武蔵?), named after an ancient Japanese province,[1] was one of two Yamato-class battleships[N 1] built for the Imperial Japanese Navy, beginning in the late 1930s. The Yamato-class ships were the heaviest and most powerfully armed battleships ever constructed,[3] displacing 72,800 long tons (74,000 t) fully loaded and armed with nine 46-centimetre (18.1 in) main guns. Her secondary armament consisted of four 15.5-centimetre (6.1 in) triple-gun turrets formerly used by the Mogami-class cruisers. She was equipped with six or seven floatplanes to conduct reconnaissance.

Commissioned in mid-1942, Musashi was modified to serve as the flagship of the Combined Fleet and spent the rest of the year working up. The ship was transferred to Truk in early 1943 and sortied several times that year with the fleet in unsuccessful searches for American forces. She was used to transfer forces and equipment between Japan and various occupied islands several times in 1944. Musashi was torpedoed in early 1944 by an American submarine and forced to return to Japan for repairs where the navy greatly augmented her anti-aircraft armament. The ship was present during the Battle of the Philippine Sea in June, but did not come in contact with American forces. Musashi was sunk by an estimated 19 torpedo and 17 bomb hits from American carrier aircraft on 24 October 1944 during the Battle of Leyte Gulf. Over half of her crew were rescued.

On this aspect, I just find subs unit Surprise Strike phase can easily represent these historical facts in the actual game.

[baron Münchhausen]

Here is some answers which can help understand why we have the actual OOB subs rules with this complexe interaction about not bringing DDs when launching an attack against a fleet protected by a stack of subs.:

@Krieghund:

@Baron:

So is there any version of OOB Subs rules which allow Submerge during First Strike and let planes be able to hit directly subs without DD, the sole condition is that defending sub choose not to submerge first (in such situation, fighter A3 or StB A4 will be considered as any single indestructible attacking Cruiser A3 or Battleship A4, because Sub cannot hit air units.)?

No.

@Baron:

In this condition DD still get a function because all freaking subs can always submerge before receiving any hits.

If all Subs rules after Revised always included both Submerge during First Strike and planes need DD to hit subs,
Does the simpler sub rule Submerge on First Strike phase with Air can hit subs without DD (if subs choose not to submerge) was ever play-tested?
Because, according to the uncorrected AA50 Rulebook,
Sub rule was easily understand that way (give hints to think about it),
subs (submerging before reg combat) becomes far less vulnerable than in Revised rules (submerging after regular combat),
and this rule is simpler: “simplifying unit interaction”.

Yes, it would make subs less fragile, but the thing that it would not do is keep subs from being used as fodder in fleet battles.  With subs being immune to air units without a destroyer, it’s dangerous to pad a fleet with subs, since all an attacker needs to do is go in without a destroyer in order to force all of his/her air unit hits to bypass the subs and hit the more expensive units.  This makes destroyers the better choice for fleet protection, as it should be.

[baron Münchhausen]

To have a better base for future discussion on any related topics to Submarines,
here is a revised version of the evolution of the main aspects about OOB Sub rules:

@Baron:

For reference, here is the OOB Submarine rule in different A&A version:

Classic:
1st Ed. 1984: A2D2M2C8, attacking Subs get Surprise Strike, cannot submerge but can withdraw in another SZ, cannot hit air.
2nd Ed. 1986: A2D2M2C8, attacking Subs get Surprise Strike, cannot submerge but can withdraw in another SZ, cannot hit air.
3rd Ed. 1997: A2D2M2C8, attacking Subs get Surprise Strike, withdraw in another SZ, defending Sub can submerge in SZ at the end of the round, cannot hit air.

Iron Blitz Edition by Hasbro and Microprose 1999, A&A 3rd Ed.:
Sub: A2D2M2C8, Surprise Strike on attack only, can submerge in SZ at the end of the round, cannot hit air.
Destroyer: A2D2M2C8 can retaliate even when hit by subs surprise strike and cancel Subs submerge.

Pacific 2001 and Europe Edition 1999:
Sub: A2D2M2C8, Surprise Strike on attack only, can submerge at the end of the round, cannot hit air, cannot be hit by air.
Destroyer: A3D3M2C12, cancel Surprise Strike and allows planes to hit subs.

Revised Edition 2004:
Sub: A2D2M2C8, First Strike (attacker and defender), can submerge at the end of the round, cannot hit air.
Destroyer: A3D3M2C12, cancel First Strike and Submerge.

Anniversary Edition, AA50, 2008:
Submarine: A2D1M2C6, First Strike, Submersible: can submerge in First Strike phase before regular cmbt, cannot hit air, cannot be hit by air.
Destroyer: A2D2M2C8, cancel First Strike & Submerge and allows all planes to hit subs.

1942.1 (2009) : Same as AA50.
Pacific 1940 (2009) and Europe 1940 (2010).: same as AA50.

1942.2 (2012) : Same as AA50.
Plus: prevent unescorted transports from offloading for an amphibious assault.

Pacific 1940 and Europe 1940 2nd Ed. (2012): same as 1942.2.