I'm very much against including heavy subs as a separate class. The STO class (the I-400's) were the class designed to carry 3 aircraft. Only three were completed. A fourth was lanched but never completed. This represents a fringe element at best. Not only that, consider the aircraft it carried had only a 640 mile range. You're only asking for exploits by including these as a separate class.
I think It's a nice addition, Japan for example built no less then 33 submarines capable of launching float-plane spotters. And heavier versions of Submarines existed in most other navies too, like the French Surcouf or US Narwhal/V-Boats.
I was a little bit startled when I saw that you where including this kind of submarines. Many navies experimented with these kinds of submarines but none with overall operational sucess. Then the logic fails when ingame this subs are the best subs you can build. (if this i right
)
Japan for example made 3 I-400s
*, namly I-400 at Kure, and I-401 and I-402 at Sasebo. One of these was converted to a tanker and never had an airplane in its hangar. The two remaining u-boats were able to carry three Aichi M6A Seiran aircraft, each carrying an 800 kilogram (1,764 lb) bomb 650 miles (1000 km) at 295 miles per hour (474 km/h). The u-boats also carried enough fuel to go around the world one-and-a-half times.
But the main question is; how good a u-boat is this. No one knows because it never saw action. So it is guesswork. But common sense tells us that thes u-boats should have better detection than others. But it's also at an disadvantage in other aspects. It's woundrable when the airplanes are on their way in or out of the hangar. Other vessels can also know of its presence when they themselves see the airplane.
On the other hand IJN had altogether 47
* submarines built with the capability to carry seaplanes. Thes u-boats were among others the B-1 class (aka I-15 class) which 20 were built. These series was rather successful, especially at the beginning of the war. I-26, in 1942, crippled aircraft carrier USS Saratoga. I-19, on 15 September 1942, fired six torpedoes at aircraft carrier USS Wasp, two of which hit the carrier and sank her, the remainder damaging battleship USS North Carolina. I-25 conducted the only aerial bombings ever on the continental United States in September 1942
The French navy built the Surcouf
*. It was ordered to be built in December 1927, launched 18 October 1929, and commissioned in May 1934. It served as a convoy escort but I havent found any reports of it being engaged in combat. It carried one Besson MB.411 which was a two-seat spotter and observation floatplane, designed by Besson. Maximum range was 400km. But again, since it allegedly never saw action, its performance remain guesswork.
The Royal navy built 3 M-Class u-boats one
* of wich was converted to carry one Parnall Peto seaplane. The U-boat was lost supposedly because of water entering the hangar shortly after surfacing. After the loss of M2 the Royal Navy abandoned submarine-launched aircraft. This was in 1932.
The US navy built a group of nine V-boats
* between 1919 and 1934. Originally called USS V-1 through V-9 (SS-163 through SS-171), the nine submarines were renamed in 1931 as Barracuda, Bass, Bonita, Argonaut, Narwhal, Nautilus, Dolphin, Cachalot, and Cuttlefish, respectively. All served in World War II, six of them on war patrols in the central Pacific. Argonaut was lost to enemy action.
None of these subs had any seaplanes. The Navy had experimented with seaplanes on submarines with a prototype hangar installation on USS S-1 (SS-105) during the mid-1920s. However, the resulting increase in scouting capability was significantly offset by several additional dangers to the host submarine, and the initiative was dropped
And for the size of the u-boats they emerged as too large and unwieldy for fully successful operation: slow to dive, hard to maneuver, and easy to detect. Somewhat more serendipitously, their large size made them useful for carrying both troops and cargo on covert missions.
V-7:Early in the war, Dolphin herself made three patrols from Pearl Harbor without notable distinction, and her deteriorating material condition soon led to restricting her to training duties, first in Hawaii, and then in New London, Connecticut, for the duration of the war.
V-8 and V-9:Unfortunately, because small size severely limited their speed, endurance, and weapons load, neither boat was successful under the conditions of the Pacific war. Each did three scoreless war patrols in the central and western Pacific, and Cachalot did one in Alaskan waters, but by late 1942, it was clear both were out-classed and worn out, and they finished the war at New London as training ships. The two were decommissioned in October 1945 and broken up several years later.
The wikipeida history lesson is over. What is the point or main argument? Although these submarines existed there is only the japanese subs that can show any operational sucess. So it seems like size doesn't matter. The game tries to model the large Japanese submarines. They can be built around 39-40. It is completly wrong on two accounts. The large subs built by japan were finished in 44. The more succesfull ones the B-1 class were built around 40, but they were not large. Yes they were large in surface and sumerged displacement. But if you look closer at armament, speed, and range it doesn't strike my as an "super" submarine.
Lets se how the B-1
* compare to germanys Type IX
* U-boat which was designed by Germany in 1935 and 1936 as a large ocean-going submarine for sustained operations far from the home support facilities
B-1: Displacement: 2,584 tons surfaced 3,654 tons submerged
IX: Displacement: 1,032 t surfaced 1,152 t submerged
comment: over twice as big and three times as big submerged. But the electrical power of B-1 (2000hp) is only twice as big as IXs (1000hp)
B-1:Length: 356.5 ft (108.7 m)
Beam: 30.5 ft (9.3 m)
IX:Length: 76.6 m (251 ft 4 in) overall 58.7 m (192 ft 7 in) pressure hull
Beam: 6.5 m (21 ft 4 in) overall 4.4 m (14 ft 5 in) pressure hull
comment: nearly twice as big again.
B-1:Range: 14,000 nautical miles (26,000 km) at 16 knots (30 km/h)
(no info on range submerged)
IX:Range: 19,425 nmi (35,975 km) at 10 knots (19 km/h) surfaced, 144 nmi (267 km) at 4 kn (7.4 km/h) submerged.
Comment: althoug higher cruising speed, the B-1 has about the same range if you calculate with the speed difference.
B-1:Speed: 23.5 knots (44 km/h) surfaced 8 knots (15 km/h) submerged.
IX:Speed: 18.2 knots (33.7 km/h) surfaced 7.7 knots (14.3 km/h) submerged.
Comment: there is a ca 10 km/h in speed difference but submerged it is only 0.3 knots. So the B-1 can close on the targe faster but is more visible bacause of size. They have the same capability of evading submerged but the B-1 is at an disadvantage because of size.
B-1:Armament 6 × 533 mm forward torpedo tubes (17 torpedoes)
1 × 140 mm 50 calibre gun
Aircraft carried: 1 Yokosuka E14Y seaplane
IX: 6 × torpedo tubes (4 bow, 2 stern)
1 × Utof 105 mm/45 deck gun with 110 rounds
22 × 55 cm (22 in) torpedoes (24 in Type IXD)
Comment: B-1 has no stern torpedo tubes. Has smaller amount of torpedos and has also a much smaller deckgun. But interestlingy some of the submarines had their aircraft hangar removed, to replace it with a 14 cm gun. So those who carried aircraft had only a 50 cal deckgun. This makes the IX much more versatile in convoy raiding as the IX can finish of merchant ships with their deckgun not waisting a torpedo. With only 17 torpedos the B-1s arsenal is soon to get depleted. But the B-1 has an airplane. But as we have seen befor the airplanes advantages comes at a cost. For example; if the weather changes between take off and landing for the worse, getting the plane back to the hangar can be tricky. If the airplane is lost, well then you loose the higher detectability right away. You have to carry aviationfuel wich can be depleted long before the fuel for the subs engines is depleted. If they use the same fuel, well then the range of the sub decreases with every flight.
Summary:
By all means include the submarines. But be sure to tweak their stats to mirror how they actually performed. Also look over their stats i comparison to other submarines more closely. Size in regards to submarines always comes at a cost.
As far as airplanes and submarines, history has thought us that this was not a succesfull combination. Haveing them in the game is good for flavor but the subs should have both stenghts and weaknesses, not overall better stats than regular subs. This safeguards us against exploits. It maybe the case that you already thought of this and has already implemented this, then you can see this post as a little history lesson.
ps
Havent got the time to spellcheck and with dyslexia it can turn out rather amusing at times. But I think I mostly made my case. All info is from wikipeida.
