The jj is an empirical model that was essentially "reverse-engineered" by the author out of historical data. That is, the jj assumes ships with known accuracy shoot that way, that shell hits inflict the same damage as they historically did, that fleet doctrine directs certain tactics, that fleet capabilities/limitations are as historical, that certain formations are used, etc. The data base includes all identified (by the author) documented hits at known ranges, interpolations were added where indicated. The jj simulates battles fought between the HSF and GF in the North Sea during the period 1906-1917. The default settings assume every day is like May 31, 1916, that the post-Jutland modifications made by the British and Germans have not been made in shells, fire control, tactics, etc. though the inputs can be varied, and as they were for Dogger Bank.
The effects of various factors were integrated into the system. For example, lower range results in greater accuracy, other factors remaining constant. There are, however, many other factors. For example, lower visibility reduces accuracy even if the range to target is not changed. Without that particular factor, low visibility engagements would result in massive hit frequencies not consistent with actual experience.
Basic aspects of jj:
- Hit Placement
- Damage Inflicted
- Damage Control
- Decision Tables
1) ACCURACY - does a fired shell hit the target?
Besides visibility, other factors that affect accuracy include:
- shooter speed
- target speed
- target on fire (especially in low visibility battles)
- shooter under fire
- shooter straddled/hit target last salvo
- shooter is one of many (difficult to correct range and bearing)
- damage to shooter
- intervening smoke
Here are a few specific data points that demonstrate the effects of visibility:
- at range 12,000 yards and visibility 12,500 yards, jj outputs an accuracy modifier of 97% of the base accuracy
- at range 12,000 yards and visibility 13,000 yards, the output is 103.5% of base
- at range 10,000 yards and visibility 22,000 yards, the output is 300% of base
- at range 10,000 yards and visibility 12,000 yards, the output is 132% of base
Base accuracy is in the range of 3 - 4% at 15,000 yards with visibility about 18,000 yards. Each shooter has a base accuracy, based on each ship history (if known) and class of gun (if not).
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2) HIT PLACEMENT
The jj does not place hits the same way as other models generally do. Basically, jj (in its current form) bins hits into 4 regions by HEIGHT on a target (not LENGTH). In World War I, the battle ranges were much lower than in World War II, or even between the wars. At long range, plunging fire could have impact at one "location" and the detonation at a much lower elevation within the ship. Such hit results are not really likely with ranges generally under 18,000 yards. The jj places a hit by HEIGHT and then by position along the LENGTH.
The relative probability of a hit at a certain HEIGHT varied by range. The jj has the HEIGHTS divided into four region, called "bins." The size of the bins varies smoothly by range. At very short ranges, waterline hits are simply not likely while upperworks and superstructure hits are very much odds-on. At 20,000 yards, on the other hand, there are few upperworks hits, relatively speaking. More of the hits are on the hull and on the deck. Superstructure hits (which includes turrets) are still likely. In general, the hull and deck bins shrink as range decreases, while the upperworks bin enlarges.
This approach explains why short range battles did not always result in a lot of dead ships very quickly. Historically, short range battles chewed up everything above the waterline, but the engines and basic power plants and buoyancy remained largely unaffected. Some very swiss cheesed hulks got home or sank later than might be expected. In World War II, the very close range hits on Bismarck at the end did not sink her because they were hitting mostly in the superstructure or high on the hull. So, too, did ships like Blucher and Wiesbaden take terrible punishment while remaining afloat long after they were combat- ineffective.
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3) DAMAGE INFLICTED
The effects of hits are fires, floods, casualties, gun loss, etc. The jj has several sub- modules that run in parallel with damage control trying to mitigate damage. If a certain flood level is reached (ship class dependent), the ship sinks. If a certain fire level is reached, the ship is destroyed, considered "burned out." If casualties reach a certain level (class dependent) then the ship is considered lost. Progressive flooding and fires getting out of control are possible. If one shell inflicts very high damage, a one-shot kill is possible; such a hit is called a "Golden Twinkee" (or GT) for reasons beyond the scope of this discussion.
Beyond the basic effects (fire, flood, casualties, GT), there are various collateral damages that can occur. Such damages result in addition to fire/flood/casualties and include losses of:
- secondary gun
- steering control
- control top (accuracy degradation)
- senior officers
- speed (bow flooding)
The damage inflicted by a particular shell hit is determined by a die roll whose spread is a function of range, shell, and armor. That is, a long range 11" hit on thick armor might have a die spread of 0 - 60, while a short range 15" hit on thinner armor might have a spread of 0 - 135. The damage tables go up to ~135, with the higher rolls generally inflicting increasingly greater damage within the bin, including collateral damage additions. In the deck and superstructure bins, a GT result is possible.
Hits on flooded spaces do no additional damage, though they may complete the flooding and make recovery of the compartments more difficult. Thus, repeated hits at the same location do not always inflict more damage. This prevents the jj from being a simple "fill in the boxes and sink the ship" model.
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4) DAMAGE CONTROL
Crew efforts to mitigate damage are important in jj. Minor to moderate flood/fire damage is mitigated with high probability, but the risks of additional damage increase as the fire/ flood level increases. The chances of successful mitigation drop as casualties increase, though some casualties are not permanent (return with time). A fire must be fought, contained, controlled, reduced, and extinguished. Flooding must be contained, reduced, and stopped. Pump out of spaces is eventually possible, as is counter-flooding. A certain list level eliminates use of the main guns, but they might be regained if the list is reduced sufficiently. Significant flood levels also reduce speed, and that reduction is greatest for bow flooding.
If a fire gets out of control, the survival of the ship is at risk. There are die rolls that the ship must survive every few minutes. Magazines must be flooded, barbettes cooled, etc. on a real time basis until the fires are contained/controlled. Visible fires makes a ship more visible to potential shooters and makes their fire more accurate by increasing the maximum visibility for accuracy equations. Large visible fires can even increase the visibility to other ships in the formation, putting them also at greater risk. Additional hits on or adjacent to active fires have the chance of killing damage control teams. In such cases, damage control must be re-established, which may take time, and more damage may take place in the meanwhile.
If flooding gets out of control, then additional spaces are affected and the ship is at risk. Again, there are die rolls that must be survived, though they are not as frequent as in the case of fires. Generally, flooding is easier to contain or stop than fire, but harder to recover from.
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5) DECISION TABLES
In jj, actions by senior officers at moments of decision are decided by the roll of (generally) two dice. The possible courses of action are ranked by aggressiveness, the higher the number, the higher the aggressiveness. For example, a 10 result would be more aggressive than a 9 but less than a 12, etc. Possible outcomes generally go down to -2 and up to +16. The middle numbers generally mean no new decision was made at that moment. Each Decision Table is constructed before it is needed, with the more in advance the better. Modifiers are established to reflect changes or new facts or observations. For example, one historical Table would be should Beatty disengage from Hipper at Jutland. Any observed damage on a German ship might be a +1, while any lost RN BC might be -3. At one point in Letterstime Jutland, an RN admiral had -7 in modifiers active!
There are no GTs in the Decision Tables. That is, there are no gross blunders or acts of prescience. Thus, in a complete jj Battle of Dogger Bank, there would be no mistaken diversion of Tiger and Princess Royal towards Blucher, as occurred historically; such actions more properly belong in the "Truth Is Stranger Than Fiction" category. To have a simulation or game outcome be the result of a GT decision would tear at relevance. This principle is found in other places in jj. For example, in jj, lookouts make and report sightings consistently with only minor variations in interval. True, all topside could miss spotting a contact on the horizon for an extended period, but that would introduce a GT decision. In such situations, jj has an "early "report, a "mainstream" report, and a "late" report --- there is no NON-report or grossly tardy one.
Distant ships, other fleet divisions, other formations, etc. all build in non-trivial time delays in jj. The admiral on the fleet flagship cannot instantly have a remote formation change course, for example. As the period modeled is World war I, there is no modern radio communications and related doctrine, though wireless does get used. Generally, commands are given by flags which must be ordered, hoisted, spotted, read, acknowledged, replied, etc. before the order can be executed. These intervals were variable and are also modeled in Decision Tables similar to the timing and treatment of lookout reports.
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