On the subject of larger subs, John French on the Battlecruisers board has posted some interesting info on what he dubbed 'Battlesubs'
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Post 40
In 1913, Fisher became seriously interested in the gun armed submarine concept the Russians were reported to be considering. By 1915 this had manifested itself as the M class submarine concept with its single 12-inch gun. However, this submarine design was only a proof of concept prototype. Fisher had Vickers working on a refined follow up design plus a second design which more resembled submersible LLC’s in concept with four 12-inch guns in two twin turrets and a surface speed of 25 knots.
As I understand it, the short 24 calibre 12-inch guns in both designs retract fully into the gun house/ turret on diving with the gunports made watertight by hinged armoured hemispherical hatches. This allows the guns to be reloaded while submerged.
Leaving the alternate scenario for a moment so as to provide some historical context: Fisher did leave a brief description of how he intended the M class would be used during the war. They would be used to attack the High Seas Fleet units anchored in the Schillig Roads. They would approach the target to whatever range was deemed suitable. Due to the limited horizon of a submarine I can’t see this being any greater than 6,000 yards; and, to ensure accuracy for a high hitting probability, probably a lot less. I presume that being close enough to penetrate belt armour from out beyond whatever booms or net defence were there, taking into account sufficient water depth to fully submerge, were likely some of the factors determining range. The M class submarines would pick out their individual targets through their periscopes, align their bows in the correct direction, surface, take their shot, and immediately crash dive. Fisher states that this operation, from fully submerged, through the attack, to returning to fully submerged could be done in ten seconds by the M class boats. If true, then the enemy ability to effectively respond to this form of attack was limited.
As I understand it, the downside to the M class was their inability to reload their 12-inch guns while submerged meaning that they had to withdraw after firing one shot and surface well away from the enemy to reload before making another attacking approach or withdrawing completely. However, a second attack approach greatly increases the risk to the submarine, while withdrawing after only firing one shot limits the damage to the enemy. The Vickers Design No. 747 (first image above) solves this by allowing the gun to be reloaded while submerged. Allowing repeated attacks in relatively quick succession to maximise damage before the submarine needs to withdraw as the enemy ASW forces begin to respond. Although, with the target mounting a 12-inch gun capable of firing both HE and Shrapnel, the traditional surface based ASW vessels may not be able to achieve anything worthwhile prior to being destroyed. The obvious downside to Design 747 is the short barrel which limits AP performance. However, all this was before Jutland when the British doctrine favoured HE effect over AP performance and it may be that it was never intended to use AP shells; the prototype M Class only using 40 calibre guns as they were readily available.
It appears to me that Design 747 is the direction that Fisher foresaw the standard attack submarine evolving. Its torpedoes could deal with the large ships while its heavy gun could be used to deal with the escorts; which had become the main counter to submarines. With the very low, narrow, and flat target profile of most of the submarine hull, destroyer and torpedo boat gun armament would be ineffective against it while a 12-inch HE or shrapnel shell would be devastating against them. Design No. 745 on the other hand appears to me to be a very different concept to a mere attack submarine. This is the evolutionary route Fisher believed that the surface gun armed capital ship would have to go. By 1915 the concept of the torpedo bomber had arrived and Fisher began to form the opinion that the days of the gun armed surface capital ship were numbered. For these vessels to have any future, they needed to be able to hide from aircraft. Stealth more so than armour would provide the primary line of defence (note; both Designs 747 and 745 have AA guns included as standard – a clear recognition of the main threat to them).
[Before I go any further I need to emphasise that a lot of what I write here regarding these heavy gun armed submarines is my own speculation as records of the thought processes behind these design concepts are slim to non-existent – with the emphasis on non-existent.]
It appears that both these designs originated around about 1915 as there is specification data from about this time regarding Design 745 surviving within the Fisher Papers. As I noted earlier, there is a strong resemblance with the LLC; a warship concept Fisher became very enamoured off due to its operational flexibility and cost effectiveness. Unlike Design 747, Design 745 appears to be designed to fight it out on the surface rather than diving between shots. Her turrets are armoured, she has an armoured conning tower and an armoured deck. To aid in her protection is her very low profile and the fact that most of her hull is below the surface therefore gaining the substantial protection offered by water.
Initially I thought how vulnerable this ship would be to diving shells adopting underwater trajectories and piercing the unarmoured hull. The my brain woke up and I realised that diving shells would never be an issue to a “
BattleSub”
[Hey! I get to invent a designator for a new warship type! – if it catches on☹] as it would not be possible to engage them at a range where diving shells would be a thing. The limited horizon of any submarine ensures that any target in visual range is going to be relatively close; with ranges that ensures any shells fired at the submarine are traveling at relatively flat trajectories. This ensures that shells that fall short are more likely to ricochet over the battlesub rather than do anything else.
I posted recently in another thread (TZoli’s
Untakeable’s thread as I recall) describing how Fisher wasn’t the long-range gunnery guru of legend, but actually aimed to sneak as close to an enemy as possible before engaging. The battlesub concept gives him a vessel capable of doing this. With the development of gunnery fire-control technology by 1915, the close-range that battlesubs would have to engage at would make it hard to miss a traditional surface combatant. The battlesub on the other hand, despite the close-range, would be a very difficult target to both hit and damage. The low target profile combined with relatively light armour, that is mostly extremely inclined away from incoming fire, and with the bulk of the battlesubs volume being protected by free water armour suggests that Fisher had finally determined a method that allowed him keep expensive heavy armour to a minimum while providing a level of protection that the most heavily armoured traditional surface combatant couldn’t match. Compared to a typical battleship, a battlesub represents a very cheap gun armed combatant that can be built in large numbers relatively quickly. How effective the battlesub would actually be in combat is open to debate. However, I think that there is some potential there with the “right” design. Whether the necessary technology to produce the “right” design was there in the 1915 to 1920 period is, again, open to debate.
It must be pointed out that Design 745 is a prototype design created to explore the concept and determine the issues that follow-on designs would need to overcome. The follow-on designs would be of considerably greater capability and I suspect that there would be a return to guns capable of effectively using AP shells, and almost certainly guns of greater calibre (an unsolicited design for a battlesub was sent to Fisher in 1919 – it had 8x20-inch guns in four twin turrets). Offhand, even I can think of a method of reloading guns underwater that doesn’t require the guns to be withdrawn completely into a turret for reloading while also providing for sealing the gun ports.
Now there are clear limitations that battlesubs have that traditional surface ships don’t have. However, I suspect that Fisher expected the other part of his “New Concept Fleet” to compensate for these limitations. With the innovative developments in wireless communication Fisher was overseeing in 1915 with the BIR, both the photophone and radio, the prospect of an integrated battlefield appeared to be within Fisher’s grasp. Fisher was always more inclined toward coordinated battle systems rather than individual weapons each doing their own thing. Aviation working in close coordination with submarines would provide Fisher’s “New Concept Fleet” with an integrated battle system where the limitations of individual components are nullified by the advantages provided by all components working in close coordination.
I have mentioned in the past that Fisher (within the BIR) planned a 100 plane torpedo-bomber strike on the High Seas Fleet in Wilhelmshaven in 1915. As no plane could reach Wilhelmshaven with a torpedo from England, Fisher planned to attach hydrogen gasbags to the planes that could lift plane, torpedo and the necessary additional fuel required to allow the raid become possible – effectively a very basic, very cheap and expandable VTO
[no L] airship aircraft carrier. I have found no evidence that Fisher had any plans to develop aircraft carriers as we know them today. It is quite likely that the abortive dirigible airship aircraft carriers of the interwar period is the route Fisher would take. Even the temporary blimps with their disposable envelopes described above would allow aircraft strike targets far away from the land bases they launched from. For example, Using Halifax, Bermuda, and Jamaica as bases, even with the primitive aircraft of the period, Fisher’s “Blimp Carrier” concept
[again my own designation as there is none that I am aware of for the concept] would put the entirety of the US eastern seaboard in range of Royal Navy airpower. The obvious downside is that the aircraft of the period would not have had enough fuel in their own internal fuel tanks to return to base and would have to ditch and the crews picked up by submarine (or other recovery vessel). However, the aircraft of the time were relatively cheap and if a massed torpedo-bomber strike on Hampton Roads gutted the US Atlantic Fleet, then the loss of the aircraft involved in the operation would, in Fisher’s eyes, have been a price well worth paying.
As Britain had potential bases for launching VTO strikes and combat patrols all around the globe, Britain’s need for traditional aircraft carriers is actually very low. The “Blimp Carrier” could provide a relatively effective and cheap alternative. Land bases aren’t even required as suitable merchant ships could be charted to transport and launch the “Blimp Carrier” squadrons in wartime. An additional advantage of using the “Blimp Carrier” concept is that aircraft performance can be optimised for the strike role without having to sacrifice performance for range and some other normal necessities (e.g. no undercarriage and all associated bits required); the “Blimp Carrier” providing those capabilities. As aircraft technology develops and increased range develops naturally, then at some point the aircraft are no longer necessarily disposable and can return to base on internal fuel following the strike. Again, the practicality of all this is certainly up for debate. Certainly, improving aircraft technology in the 1930’s will lessen the usefulness of “Blimp Carriers”, but between 1915 and 1935 it is a concept that appears to offer much.
Returning to our alternate timeline scenario: Fisher lays down his prototype battlesubs in 1915 (alongside the production version of the attack subs with their single stubby 12-inch guns) and builds them within a year. During their construction, a series of more capable designs are drawn up awaiting trials results from the prototype battlesubs for refinement. The battlesubs enter service in 1916 as Fisher lays down the
Incomparable IIa’s. After extensive testing a finalised battlesub design is crafted, likely carrying 4x18-inch or 4x20-inch guns in two twin turrets. At least four are laid down in 1917 instead of the more expensive gun armed surface capital ships. It is likely that there will also be a larger number of smaller “Cruiser Subs” (something similar to design 745 but of greater capability and with more effective 12-inch guns) and a horde of Attack Subs laid down as well. With Germany defeated in 1915, Fisher gets his hands on the secrets of the Zeppelin and a large airship program begins in 1916 alongside a large procurement programme for new aircraft for the Naval Air Service.
The butterflies are swarming at this point. What will the Japanese and US response be? Truthfully, Japan cannot challenge Britain at all and that leaves the US. Will they ignore Britain and focus on Japan? Will they challenge Britain for control of the trident? By 1916 Britain’s pre-dreadnought fleet is gone. The eleven 12-inch gunned dreadnoughts are heading for the scrappers torch but their turrets and guns might be preserved for future LLC construction. Britain has fourteen 13.5-inch ships (the six
Excalibur’s in material reserve – one move away from scrapping), eight 30-knot 15-inch gunned battlecruisers, eight 30-knot 16-inch gunned high-speed battleships, and eight of the largest most heavily gunned, fastest and most expensive battleships in existence under construction. There are possibly twenty-one 12-inch LLC’s in commission or under construction: a warship type to which the US have no equivalent or counter. A huge program of heavy gun armed submarines just has just been laid down, and four of them are like nothing ever seen or conceived before and have a heavier broadside than any of the 12-inch gunned US battleships. Then there is the largest aviation procurement program in the world to consider. What does the US have in its design drawer to respond to this with? And! Can they afford it? Also, the US never fought in the war and did not benefit from contact with the Grand Fleet. They never saw inside Britain’s design thinking as they did historically with the plans for
Hood and Goodall. They have no combat experience in ASW and, in this reality, have had no access to the submarine detection equipment developed by the BIR.
If I recall correctly, 1916 was the time of the main Tillman design effort. Are any of these designs a worthwhile counter to what the British are building? Are anything from the historic US 1916 program even relevant anymore and, if so, are there enough of them? Fisher is building his behemoth battleships in two years; can the US match this building tempo? Is there anything else in the USN’s suggestions box for this period of use? What will the US response (if any) be to the battlesub?
Imaging this scenario: In the mid-1920’s, a US battleline consisting of Tillman battleships sallies forth to do battle with the Royal Navy surface fleet. Suddenly, at only a few thousand yards distance, Royal Navy battlesubs surface and start punching 20-inch AP shells through the armour belts and into the vitals of the US battleships; AP shells which are followed by a mass salvo of torpedoes from the quad broadside torpedo tubes of the battlesubs. The US escorts alter course to charge the ambushers when British Attack Subs burst from the seas and blast the US light forces with their 12-inch guns at relatively close range. Is this scenario feasible? Can the US surface fleet win, or even just survive, such an encounter: bearing in mind that, just beyond the horizon, there are multiple squadrons of Royal Navy aircraft, both fighters and bombers, just floating in the sky, dangling from their “Blimp Carrier’s”, with their engines switched off, just waiting for orders from the British admiral, surveying the battlefield from his dirigible airship flagship, to jettison their balloons and engage the enemy!
As I said, the feasibility of Fisher’s vision is open to debate; but it sure makes for some very intriguing “what if?” scenarios.
