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- 2 Pump Ships -


Ships mounting 2 pumps seems to have gained popularity in recent years. The allocation of offensive to defensive units has been left to captain preference for the vast majority of the history of the hobby. For the most part, captains have historically chosen to use 1 pump and the rest guns. To my observation, the recent trajectory of relative increase in multi pump ships started in 2009 when Jeff put 2 pumps in his IJN Mutsu (Nagato) in order to combat the relative effectiveness of the USS North Carolina. At that time the North Carolina with triple stern guns was widely considered the best ship in the hobby and there were a number of North Carolina captains with highly functional ships that were causing buoyancy problems especially for the Japanese battleships. It is fairly well established that putting damage into the flared bow is highly effective at forcing these ships to become unable to effectively maneuver and sink. As I write this article, the Nagato remains the prime example of a ship that is most commonly set up in this fashion, however other ships have also benefited from and used 2 pump setups. The larger ships (Richelieu, Bismarck, Vanguard, Yamato, Iowa) are able to be more competitive with 2 pumps in that these very large ships can more safely take damage in an otherwise easy to hit target, but also are able to sacrifice a smaller percentage of total offensive capacity in order to use another pump. For the most part, only a hand full of captains even in recent years have used 2 pump setup in class 5 ships. It is much more common in class 6 ships. In class 4, it seems to be too much of an offensive sacrifice to mount 2 pumps, though being able to split a 4.5 unit ship into 3.0 guns and 1.5 pumps could be viable.


Due to the increasing popularity of using 2 pump ships, the performance differences and how they should function and be balanced are being called into question. The intent of this article is to try to use data to better understand how these ships are performing. I have been able to compile the scoresheets from Nats 2015-2020. I included each complete battle by a captain in a single ship (2 sorties completed or sunk in the first or second sortie) as a single data point. Campaign, night battle, one-on-ones, challenge battles, and ships that withdrew from combat were excluded. There were 755 data points across 6 years.




“How popular are two pump ships and is there change over time?”

Of the 755 data points spread over 6 years, 126 (16.6%) were two pump ships, 629 were 1 pump ships. As a function of time, there seems to be relative stability in recent years without a clear trend.  


“What ships are being fit with 2 pumps?”

As a percentage of all ships battled in this time period, a 2 pump Nagato has the more entries than any other ship and constitutes 5% of all of the ships at Nats. Nagatos have used 2 pumps 69% of the time and 1 pump 31% of the time. QE has the 2nd most entries but it is less popular to battle a QE with 2 pumps than with 1 pump. The Bismarck was used some with 1 pump, but mostly with 2 pumps. The very large ships with 8 battle units were exclusively used with 2 pumps in this data set. There was only one class 4 ship to use 2 pumps.


“Are certain captains heavily influencing the data?”

Interestingly enough, roughly half of the 2 pump use has come from just 5 captains (60 out of 126 entries). Only these 5 captains have used 2 pump setups in multiple Nats. Tyler used two pumps 23 times (5 in Nagato – one Nats, 17 in QE – 3 Nats), Mark 14 (all Nagato), Jeff 10 (5 Nagato, 5 Yamato), Will (all Jean Bart over 2 years), Carl (4 Rodney, 2 Yamato). Additionally, 3 captains account for 24 of the 39 two pump Nagato entries. All other captains not listed below used a 2 pump setup for just one Nats event. Tyler alone accounts for 18% of all of the 2 pump ships used spread across 4 of the 6 Nats.


“Are the Axis or Allies the biggest user?”

The axis are more prone to use 2 pump setups, 19% of the time vs the Allies’ 14%. Though in raw numbers this is only 8 more occurrences (ie, one captain at 1 and ˝ nats).


Damage Taking


“Does having 2 pumps make it less likely to sink?”

“How much more damage can a 2 pump ship take?”

I have averaged the holes a 2 pump ship takes in a battle regardless of if they sink or not, how many they take when they sink, and how many they take when they don’t sink. To sink an average 2 pump ship it takes 103 holes, vs the 76 holes it takes to sink a 1 pump ship. 27 additional holes is roughly a 35% increase. It would seem counterintuitive that it doesn’t double or even come close to doubling damage threshold of sinking.


Another useful way to view the data is to consider each battle as an individual entry and normalize the data. This allows us to make a graph that can aid in understanding the numbers. The standard deviation is quite wide, meaning that the disparity for all ships is very massive, the difference between high and low achieving ships regardless of if they sink or not and regardless of how many pumps they use is high. Interestingly enough, the degree of disparity, ie the variability in how many holes it takes to sink a 2 pump ships is slightly higher as compared with 1 pump ships which is slightly more consistent.



“What if you exclude very lightly damaged ships”

To adjust for light damage sinks, I have excluded all ships that sank with less than 50 above and/or 20 below and ran the data again. This is intended to remove the lightly damaged outliers. Regardless of number of pumps, it is surprisingly common for ships sink with light damage due to captain error, poor ship design, bad luck, or systems failure. After the adjustment, the number of holes it takes to sink a ship expectedly increases but the absolute disparity remains near identical, 124 holes to sink a non-lightly damaged 2 pump ship vs 99 holes to sink a non-lightly damaged 1 pump ship. The 25 holes however translates to a lesser relative difference, in that having 2 pumps only increases survivability by 25% compared to 1 pump ships.


“What if you compare within a class?”

Similar Results are found if Class 6 (Excluding Vanguard, Iowa, Yamato) and Class 5 are compared amongst themselves. To sink a class 6 ship with 2 pumps takes 126 holes vs 102 holes for a 1 pump ship. To sink a class 5 ship with 2 pumps it takes 121 holes vs 104 holes for 1 pump ships. Comparing ships by class maintains the relative risk reduction of sinking with adequate damage by only 25% if using 2 pumps. It should be noted that light damage (<50 above and <20 below) was similarly excluded in this series.


“What if you compare a ship only to itself?”

The QE was used because it has the broadest data set (most captains, several entries with 1 pump, several with 2 pumps). This is raw data only, light damage and light damage sinks are included. The limitation is that only 2 captains used a 2 pump setup. A few interesting findings are that Andy’s 2 pump QE sank with less damage and more often as compared to when he ran 1 pump in it, though the damage taken when he didn’t sink was higher in the 2 pump setup. The rate of sinking is 35%, identical for 1 and 2 pump ships. The average damage taken to sink the 2 pump setup in this ship was 102 as compared to the 88 for the 1 pump setup. The difference of 14 holes translates to 16% increase in damage required to sink with 2 vs 1 pump. The standard deviation of holes taken to sink is a whopping 28, indicating a very large disparity in this data. Bob’s, Andy’s and Brandon’s one pump setup all beat the average for the 2 pump setup when they sink. Like wise several captains/ships are on the very low side of the spectrum. When the data for all ship/captain combinations is normalized (see graph) it becomes very apparent that all QE’s are not created equally.



I’ve also divided the data for each battle to have its own data point rather than using the average and sorted by sinks/floats for the QE and compared average holes for 1 vs 2 pumps. The data would indicate that a QE’s experience if not sunk is identical with 1 or 2 pumps, average holes are 74 regardless. However, if 2 pumps are used they will take an additional 24 holes to sink as mentioned above. The charts below show the data normalized. Again, with 1 pump or with 2 pumps there is a massive disparity in damage required to sink but generally speaking fewer really lightly damaged sinks for 2 pumps though a cluster around the mean is clear. Again you can see that several 1 pump QE’s out perform some of the 2 pump QE sinks.  




“Does the likelihood of sinking or surviving with light vs heavy damage change based on number of pumps?”

As alluded to above, a way to interpret data that seems to generally be informative is to try to group ships by light vs adequate damage. The intention is to remove lightly damaged outliers from the data. I approximate that most class 4 and higher ships should be able to in most scenarios survive less than 50 above and 20 below holes. For the purpose of sorting data, I categorize these as “easy sinks” if they don’t meet these criteria and sink and “easy float” if they don’t meet these criteria and don’t sink. Ships that sink with at least 50 above and/or 20 below are “tough sinks,” meaning that there was less likely a system failure or poor design alone that lead to the sinking of the ship, and similarly “hard float” if they took adequate damage but did not sink. Of the 126 ships with 2 pumps, half of them float despite taking adequate damage, whereas 29% of 1 pumps did so. As far as light damage, 5% of the time a 2 pump ship takes to the water it sank with light damage, whereas 10% of the a 1 pump ship goes to battle it will sink with light damage.




Regardless of the various criteria applied (class of ship, all data, light damage excluded), it takes roughly an extra 25 holes to sink an average 2 pump ship as compared to a 1 pump ship. At maximum this is 35% more damage/holes, but in reality it is closer to 25% more damage when lightly damaged ships are excluded. This number is really important in that it is indicating that adding a pump no where near doubles damage taking capacity.


For all ships regardless of if they sink or float, the average holes a 2 pump ship takes is 91, as compared to 62 for a 1 pump ship. The difference being 29 holes. Generally speaking, when a 2nd pump is added, a 50 round stern gun is removed. At most 30-50% of an average sten gun shots will make a hole in a target. Therefore, by removing a gun and adding a pump, you are in effect taking on average 29 holes into your ship and removing 60-100 holes of damage (50 rounds x2 sorties) to the other team. For the average captain this is a significant net negative in terms of hole scoring alone. However, I believe a high performing captain can get over 50% of a stern gun or stern sidemount to hit and if they can otherwise be effective on the water and not sink, in this situation may just make up for the holes they take in return.


2 pump ships are not unsinkable, but do sink less often. 22% of the time a 2 pump ship goes out to battle, it gets sunk. This compares to 31% of the time for a 1 pump ship. Improved survivability is not unsinkability, though the relative likelihood of sinking is cut by 1/3. It is very important to realize that adding a pump doesn’t decrease your chance of sinking by 1/2 as could otherwise be theorized. The disparity actually shrinks massively when excluding lightly damaged ships, as 17% of 2 pump ships sunk vs 21% of 1 pump ships sunk, which is really only cutting the relative risk of sinking by 25% by adding a 2nd pump.


2 pump ships are less likely to sink with light damage. 5% of the time a 2 pump ship goes to battle it sinks with light damage as compared to 10% of the time for 1 pump ships. This is the category with the larget relative benefit gained by using 2 pumps. By adding a 2nd pump you decrease the likelyhood of sinking with light damage by 1/2. I would guess that a fair bit of this is having a larger margin of error for pump system failure.


Having 2 pumps appears not to be a deturrent to getting shot. I’ve heard that some captains believe it isn’t worth engaging with 2 pump ships because damage dealt to them is less likely to cause a sink, so they should just be avoided. And as already stated, on average a 2 pump ship will collect 29 more holes than a 1 pump ship in any given battle. The data also indicates 2 pump ships survive with light damage only 27% of the time, where as 1 pump ships take light damage more often, 39% of the time. I would expect that some of this may be due to a higher level of agression 2 pump ship captains feel that they can safely battle with.


The disparity between different captains and different builds is highly appearant in the QE specific data set above. It would appear that some captians can be just as tough or better in a 1 pump QE as a 2 pump QE. And some 1 pump QE captains are outside of 1 standard deviation below the mean with damage when they sink. This argues to the point that I often make, is that the captain’s ability to build and battle are far more important than the ship selection. There are certainly ships that are inherantly more powerful than others, however the disparity in captain ability is much more broad than the disparity in ship power. Having battled on both Axis and Allied fleets (at Nats I’ve battled Axis 5 times: Derfflinger, Nagato x4, and Allied 5 times: Minneapolis, Bob’s QE, Barham x3), in my opinion the Axis/Allied disparity of powerful ships is balanced.


Limitations and things that would seem true but are difficult to conclude from the data.


Various factors seem to be true but can’t be measured by the data alone. The challenge when a direct observation seems cleraly to be pointing to a certain conclusion is that true causality can be more complicated. The challenge in that is related to human bias, we tend to believe things we see with our own eyes as we interpret them, even though we don’t have clear reproducable evidence to support it. That’s where the data can help. Before doing the math for instance, I would have figured two pumps make it possible to take 50-70% more damage before sinking rather than the 25-35% the data indicates.


Though there are 755 data points, there are certain limitations due to the size and properties of the data set, especially if any specific smaller subset is considered. Tyler is a lot of the 2 pump data (18%). 2 pump Nagatos are primarily 3 captains who I would consider to function highly in any ship they bring, and 5 of the data points are a different captain drivng said Nagato. As another example, Tyler and Andy account for all of the 2 pump QE data points.


The data can’t describe how captains drive their ships. In general I would expect 2 pump ships to be captained in a more aggressive way. Also, I would expect that 2 pump ships are more likely to mauver better with higher amounts of damage. The late stages of battle may be heavily influenced by 2 pump ships that have a little more staying power. The damage/sinks they cause are not going to show up in the data, but observations of how the water is controlled may have different optics.


The 2 pump data is not only heavily influenced by a small number of battlers, but I would also argue that the optics of 2 pump ships in general are heavily influenced by what we experience pond-side, though data may seem to indicate otherwise. For instance, I would expect that a fair number of people didn’t realize there was a Kongo in 2018 with 2 pumps, even those at that event battling against it. On the flip side, lot of the 2 pump Nagatos have been Jeff’s builds, driven by Jeff, Mark, or Johnny. Most people who have been on the water with them would recognize that these specific ships are very highly tuned and the captains are higher performing regardless of ship.


Another valuable viewpoint is how 2 pump ships perform at local events and regionals. There are a few specific issues with this that we will not easily be discernable from this or any data set. One is that some regionals allow for sunk 1st sortie ships to patch and come back in, or some times have 3 sortie battles. Though I have access to it, using regional battle data would be inconsistent with the way the rest of the data interacts and as such was not used. Also, the way that battlers tend to play at regional events is often more aggressive and probably would skew the data differently depending also on how many battlers are at an event. Additionally, the optics of a very highly tuned ship captained by one of the best battlers in the hobby at a small regional battle for instance might lead to the view point that the ship is too powerful, when in fact the actual issue is that the disparity of building and battling skill is more exagurated at smaller events, when it feels like you take a beating from said battler multiple times per weekend.


Part of the subtle effectiveness of using 2 pumps actually comes from enhanced offensive capability that results when exchanging stern firing guns for a sidemount. A lower damage yielding gun is exchanged for a higher damage yielding gun in addition to adding a pump. As I pointed out above, this may actually lead to an average captain becoming net negative. Also in some ships, specifically 3 turreted ships, using 2 pumps in exchange for trying to mount more sidemounts leaves very few possibilities for reasonable gun setups. This is especially true for the Allied class 6 ships, and it generally isn’t a well-balanced setup to do this. The North Carolina is a great example of this. The often discussed Axis/Allies disparity in which ships are naturally best suited to use a 2 pump setup is in my opinion part of the inherent difference between the Axis and Allied ships in general and has value in and of itself. Its more interesting if there are different strengths/limitations that seem to cluster by nation. In years past there was a commonly held view point that the Axis were under gunned due to lack of triple stern gun ships. In more recent years the discussion has shifted to the Allies feeling disadvantaged by trends in the hobby due to the lack of fast ships that use stern sidemounts and ships that can more naturally utilize two pump setups. Just as there was a response to triple stern guns, there is likely a response to two pump ships that is currently being under-utilized. 


Again, it is very important to realize that any specific ship or setup is only as good as the person who built it and who is captaining it. Even within the data above, there is a high level of disparity amongst 2 pump ships in how much damage they take to sink. Something that I observe in the data that is difficult to quantify is the high number of what I would consider top battlers in the hobby also opting to use 2 pump ships. All of the captains who have used 2 pump setups in the data I have also seen in 1 pump ships over the 14 years I have been in the hobby, and all of these captains I would also consider highly effective battlers in any ship they bring. This gets back to optics. Highly function captains are better able to get the most out of any ship build, including 2 pump designs. And highly functioning captains seem to be seeking advantages by using this design.


Tyler, 3/17/2021



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