Imperial Military Calculations Revisited
Posted: 2014-06-17 09:07am
This article shall be based upon the work done here: http://www.daltonator.net/fanfics/essays/impfleet.txt by Commander Thelea.
First of all, let me just say that I admire the work that Commander Thelea did on his/her essay-article thing on the Imperial Fleet size. Now, before I even get started, I'm going to outright ignore anyone who starts pipping up about “b-b-b-but it's not canon” or some other BS. It was canon back then and so long as it takes place between ANH and ROTJ, then I consider it to remain cannon. I am not including any computer games into this. Only written books (largely from the WEG material and the new Essential books). That said, this is not a rebuttal to Commander Thelea's work, but rather a correction and compliment to it. I believe that Thelea was right, to an extent, that most people are sadly underestimating just how large the Galactic Empire was and how mighty it's military equally was. Let's lay a little groundwork now...
Now just how big is the Galactic Empire? The Essential Atlas (2009) says that, “at its peak” (probably just before and just after the Battle of Yavin) the Galactic Empire “consisted of 1.5 million member worlds and sixty-nine million colonies, protectorates, and puppet states.” The newer (2013) Fantasy Flight Games “Edge of the Empire” RPG core rulebook says “...galactic cartographers and astronomers place the number of habitable systems at 3.2 billion. Of those, only 69 million or so have sufficient population for Imperial membership, and, finally, only about 1.75 million planets are fully represented and integrated into the Galactic Empire.” The West End Games Star Wars RPG game states that the Old Republic “eventually embraced over a million member worlds, and countless more colonies, protectorates and governorship. Nearly 100 quadrillion beings pledged allegiance to the Republic in nearly fifty million systems.” Now there is no suggestion in the WEG book that says when the switch from Republic to Empire was made that worlds were lost – if anything, they gained even more through outright expansionist conquest. The FFG book mentions only member worlds but hints at a larger amount of what could be 'colonies, protectorates, and governorships.' The Essential Atlas (which most might be more willing to trust) gives us that the GE “consisted of 1.5 million member worlds and sixty-nine million colonies, protectorates, and puppet states.” For all intents and purposes, I plan to follow mostly with the Essential Atlas.
Now here is where I mention the importance of recognizing the Ruusan Reformations, as described in the Essential Guide to Warfare (2012). “To make the Senate more governable, Valorum consolidated its millions of sectors into 1,024 regional sectors, each with its own Senator, though political necessity forced him to carve out exemptions for powerful worlds in the Core and Colonies...” It is important to note this, since it is the basic building block for the military organization of both the Republic and the Galactic Empire. So we have 1,024 regional sectors, each of which has its own Sector Fleet and Systems Forces (the distinction of which I will explain later).
According to the novel duology by Timothy Zahn, the most important of which is “Visions of the Future,” the Empire of the Hand is a section of the Unknown Regions that consists of an estimated 250 sectors. While many Imperial fluff supporters will be willing to include these 250 sectors into the accounts of the Galactic Empire’s power and resources, I believe it would be fallacious to do so. We know that the EotH only came to the extent of 250 sectors at the point of the novel, which takes place 19 years ABY (after the battle of Yavin). As such it’s resources and material cannot be included into any account of the Galactic Empire – which I will henceforth see as a separate entity. There is also no reason to believe, considering the EotH’s architect (ie Grand Admiral Thrawn), that its defenses would be organized on the same lines as the Galactic Empire’s own sector group fleet order of battle, this due to the fact that it is well recorded that Thrawn was continually given sub-par reinforcements and support from Palpatine – starting his venture with a single Imperial Star Destroyer! There is also the major influence of the Chiss upon the EotH, who accounted for a great percentage of manpower and resources to the creation and continued defense of the EotH. As such, the 250 sectors and their supposed defenses forces will not be taken into the calculations herein. Nor will I include any of the supposed “Deep Core conquests” that Thelea makes allusions to but makes no serious mention of in terms of sources.
There seems to be a distinction between sector groups and fleet assets, perhaps lending some credit to Thelea’s assertion that the Imperial Starfleet and the Imperial Navy are two separate entities. However the size of said assets may vary, as I will try to ascertain below.
According to the WEG “Imperial Sourcebook Second Edition” a system force “is commanded by a systems admiral, also known as a commodore. A system force is responsible for several systems, the admiral being in charge of organizing and coordinating all of his ships throughout a sphere of command spanning hundreds of light years and dozens of worlds, the normal method of communication being no faster than the ships themselves.”
Further, there is the distinction within the WEG material between a Fleet and a System Force. It says clearly that a Fleet is “designated as a ‘sector resource,’ which means it should be available for action anywhere within the sector. A fleet is the smallest unit transferred between sectors. All fleets have a force technical service and force support under their command.” Not only does a Fleet have a different deployment mission but it also has a separate supply and support chain. That is a very clear and indisputable indication of the Imperial Starfleet and Imperial Navy being separate entities – to which System Forces are the building blocks of Starfleet and Fleets are the building blocks of the Imperial Navy. Because the regional forces that would be collected to create the Grand Army of the Republic and from that into the Imperial Military, it is only natural that the organizational structure would remain similar, and as such Imperial Fleets are organized based on a similar structure to system forces, but are not of them. There is also the addendum that certain moffs and grand moffs (such as Tarkin and Carlinson) “could easily have 15 additional squadrons attached to their sector group HQ.” Then there is the last sentence of the Sector Group Organization: “Thousands of Sector Groups are at the Emperor’s command as he seeks to bring the galaxy firmly under his control.”
The differentiation between System Force and Fleet, the fact that moffs could gain “easily” an additional 15 squadrons to their Sector Group HQs (if that’s easy, I wonder how many they could gain through ‘tough’ negotiation), and that it mentions “thousands” of Sector Groups (when there are barely 24 more than a thousand sectors in the known galaxy) it is clear that Thelea was right. But that is not to say that all sector groups were equal (more on that below).
The reason I point out the specification for defining what a system force is, is because of the next sentence: a system force is organized along force pools, available resources categorized by general mission type. While they have a set organization on the OB, a commodore is expected to reform the constituent elements of a pool to tailor the detail to the mission.” Clearly this means that a systems admiral does not have the resources at all times to form every type of System Force (as will be detailed below) but rather he has the constituent parts to make up one or another such system force as the needs of his particular defense and patrol requirements are. His/Her total amount of ships should therefore be calculated as being thus: 3 Imperial Star Destroyers, 6 to 12 torpedo spheres, 30 to 48 cruisers or frigates, 60 to 80 corvettes, 35 to 50 light cruisers, 8 to 16 specially modified recon light cruisers, 4 Evakmark-KDY transport vessels, 4 strike cruisers, 8 FTS Evakmark-KDY transport vessels, 16 Escort Frigates, and 100+ support ships. A System force can therefore muster a (at best) maximum total of 217 warships, 12 torpedo spheres and 112 support ships.
Sector Groups, of which Systems Forces are a constituent part, make up (according to WEG) at least 2,400 ships, 24 of which are Star Destroyers. If we know that each System Force will always contain 3 ISDs, then that means there are roughly 8 System Forces within a single sector, to whit there are: 24 ISDs, 96 torpedo spheres, 1,712 other combat ships and 896 support ships in a single sector group; which means that of the 1,024 sectors in the Galactic Empire, there are an estimated 24,576 ISDs, 98,304 torpedo spheres and 1,753,088 other warships, and 917,594 support ships within the Imperial Starfleet.
In his/her calculations, Commander Thelea included Sector Fleets and System Forces together, which was I think his mistake. Instead of seeing the Sector Fleets and the System Forces as a separate entity, he saw them jointly as being the Imperial Starfleet (aka Coast Guard) and his own estimations of the “25,000 Star Destroyers” comment to be the Imperial Navy (aka the offensive line). He even includes oversectors in this calculations – that being a mistake since Oversectors were not “new” but were rather special political and military zones of authority. No new fleets magically appeared with the creation of the oversectors – it was purely an administrative adjustment to the regional governor decree and allow commanders to cut through red tape.
Now Thelea's argument for the size of the Imperial Fleet/Navy (offensive line) is based on his own observation of Darth Vader's “Death Squadron” (as seen in TESB) and a computer game that mentions a battlecruiser (larger than a standard ISD, but not an SSD) appearing in the aftermath to help chase the Falcon. He then postulates that three ISDs must therefore be an escort for the Executor and the other two must be an escort for the unnamed and only mentioned battlecruiser. However he completely discounts the fact that Death Squadron was a special task force formed by Darth Vader for the sole purpose of hunting down the Rebel Alliance and his son, Luke. In the same way that various Moffs and Grand Moffs had their own personal squadrons that existed outside the normal Order of Battle, Darth Vader as the Commander in Chief of the Imperial Military had his own elite squadron as well. To try and postulate the size of the Imperial Navy based on a misinterpreation of Death Squadron's reason for existence and a single mention in a computer game (of which all such sources are discounted) is reckless to say the least. There is also the dubious figure he states that the Imperial Navy had 25,000 ISDs...but ONLY six – SIX – torpedo spheres. That big of a distribution between capitol ships and siege platforms, especially after he showed how many a Sector's System Forces were suppose to (on paper) maintain is just...it just don't make any sense.
When Thelea talks about Imperial Member World Defense Fleets, he mentions the two Golan II platforms that were defending Coruscant and uses that as the measurement of the rest of the GE. That is a huge mistake in my opinion. It is part of several cannon sources that some systems were better guarded than others. Coruscant, Kuat, and Corellia were all far more heavily guarded that Alderaan, Sluis Van, or Valc III. He also doesn't take into account the various worlds, such as Carida, that might be considered “fortress worlds.” So to assume that all is equal across the board, even at best, would be so absurd as to be a step beyond fallacy.
For example, as he also cites, the Bakuran Defense Forces consisted of a single Carrack-class Cruiser, 6 Corellian Gunships, 3 Marauder-class Corvettes, 5 IR-3F patrol ships, 72 TIE fighters, and 5 TIE bombers. That might be what we can expect from a backwater colony like Bakura, but likely this is not identical to all other colonies. Indeed, in the Poln System of the Candoras Sector (the sector capitol no less) the only Imperial defense forces are four “antiquated” Dreadnought-class Heavy Cruisers and “some smaller ships.” (Choices of One) Clearly there is no cookie-cutter fit to all of the colonies, protectorates, and governorships that existed outside of the official member worlds of the Galactic Empire. And while Thelea stresses that he isn't trying to create a cookie-cutter image, he inevitably does so in trying to form his ultimate calculations.
I personally believe that the number of Torpedo Spheres is exaggerated. It says within the material that there were “at most” 2 Torpedo Spheres within a Torpedo Line, of which a Bombard Squadron was – at paper strength – supposed to have 6 Torp Spheres. Seeing as how most fleet actions were bent around pursuit of rebels and pirates and less about planetary sieges (especially after the end of the Clone Wars and the final stages of the Outer Rim Sieges in the early Imperial years), I am led by sheer military practicality to believe that the number of Torpedo Spheres that the Imperial Military possessed never numbered more than 10,000 at best. Whether some might have been mothballed or otherwise deployed in the roll of orbital stations (removing their mobile ability) is not stated anywhere, but in realistic military sense would make for a better explanation.
Now, for a galaxy-spanning government that has between 1.5 million member worlds, as well as sixty-nine million colonies, protectorates and puppet states (Essential Atlas), to as many as (according to the new Fantasy Flight Games “Edge of the Empire RPG Core Rulebook) “1.75 million planets [that] are fully represented and integrated into the Galactic Empire” this military seems small. That alone means that each individual ISD would be, in some aspect or another, responsible for protecting and policing 61 inhabited worlds. Even with the additional warships (cruisers, frigates, corvettes, and smaller) there would barely be 1.1 ship per planet. As such, I believe that these numbers give credence to the idea that the Imperial Starfleet is a type of “Coast Guard” or purely Self-Defense & Policing Force, whereas the Imperial Navy is the actual fighting crème-la-crème of the Imperial military and represents its offensive capability.
It is quite easy, considering the Galactic Empire’ size, political foundation, and strong economy that it could produce twice the number of estimated ISDs and bring about a total number of at least 50,000 ISDs – half used for Sector defense and police work, and half used for offensive and cross-sector-border pursuits.
Now, concerning Star Destroyers, we have to realize that the Galactic Empire built its military up from the already considerable size of the Grand Army of the Republic. It is a stone-cold fact that the Republic ordered and received over a thousand Acclamator-class Assault Ships (early prototype to the later wedge-shaped ships) and thousands of sub-classes to that design. They also built and received thousands of Venator-class Star Destroyers. In the movies and the Essential guides it is made clear that almost a thousand Venator-class SDs took part in the Battle of Coruscant where General Grevious made his bid to capture Palpatine – a thousand! All while the Republic was on the frontiers fighting with 20 “sector armies” that spanned across distances that can only be described as friggen' gargantuan, what we'd consider to be dozens of normal regional sectors. You could probably argue that these Republic Army Sectors were the inspiration for Tarkin's “special oversectors.” Otherwise, if you try to take it at face value, you get into the minimilization craze brought on by Karen Travis (let's not have that argument again, shall we?). So clearly, we have thousands, possible tens of thousands, of Acclamators, Venators and even the eventual rise of the Victory-class Star Destroyers, all ready for use by the Galactic Empire.
There is no indication by either the WEG, FFG, or Essential guides that the Imperial Military made a marked distinction between the various classes and subclasses of Star Destroyers. So when I say that there were at least 50,000 Star Destroyers, it's quite possible that a 5th of them are older models and such.
Long story short, of the 1,024 sectors in the Galactic Empire, there are an estimated 24,576 Star Destroyers, 98,304 torpedo spheres and 1,753,088 other warships, and 917,594 support ships within the Imperial Starfleet. (Coast Guard)
The Imperial Navy (offensive line) is another matter. Seeing as its late for me, I'll do those calculations tomorrow and make a second post. I've already explained my position in support of and opposition of Thelea's assessment and here with my own. It does not take into account the local defense forces and privately raised (non-Imperial) forces that planets that are aligned with the Galactic Empire, but left to their own defense issues, may or may not have. This is solely for the Imperial Starfleet and Navy.
Spoiler
First of all, let me just say that I admire the work that Commander Thelea did on his/her essay-article thing on the Imperial Fleet size. Now, before I even get started, I'm going to outright ignore anyone who starts pipping up about “b-b-b-but it's not canon” or some other BS. It was canon back then and so long as it takes place between ANH and ROTJ, then I consider it to remain cannon. I am not including any computer games into this. Only written books (largely from the WEG material and the new Essential books). That said, this is not a rebuttal to Commander Thelea's work, but rather a correction and compliment to it. I believe that Thelea was right, to an extent, that most people are sadly underestimating just how large the Galactic Empire was and how mighty it's military equally was. Let's lay a little groundwork now...
Now just how big is the Galactic Empire? The Essential Atlas (2009) says that, “at its peak” (probably just before and just after the Battle of Yavin) the Galactic Empire “consisted of 1.5 million member worlds and sixty-nine million colonies, protectorates, and puppet states.” The newer (2013) Fantasy Flight Games “Edge of the Empire” RPG core rulebook says “...galactic cartographers and astronomers place the number of habitable systems at 3.2 billion. Of those, only 69 million or so have sufficient population for Imperial membership, and, finally, only about 1.75 million planets are fully represented and integrated into the Galactic Empire.” The West End Games Star Wars RPG game states that the Old Republic “eventually embraced over a million member worlds, and countless more colonies, protectorates and governorship. Nearly 100 quadrillion beings pledged allegiance to the Republic in nearly fifty million systems.” Now there is no suggestion in the WEG book that says when the switch from Republic to Empire was made that worlds were lost – if anything, they gained even more through outright expansionist conquest. The FFG book mentions only member worlds but hints at a larger amount of what could be 'colonies, protectorates, and governorships.' The Essential Atlas (which most might be more willing to trust) gives us that the GE “consisted of 1.5 million member worlds and sixty-nine million colonies, protectorates, and puppet states.” For all intents and purposes, I plan to follow mostly with the Essential Atlas.
Now here is where I mention the importance of recognizing the Ruusan Reformations, as described in the Essential Guide to Warfare (2012). “To make the Senate more governable, Valorum consolidated its millions of sectors into 1,024 regional sectors, each with its own Senator, though political necessity forced him to carve out exemptions for powerful worlds in the Core and Colonies...” It is important to note this, since it is the basic building block for the military organization of both the Republic and the Galactic Empire. So we have 1,024 regional sectors, each of which has its own Sector Fleet and Systems Forces (the distinction of which I will explain later).
According to the novel duology by Timothy Zahn, the most important of which is “Visions of the Future,” the Empire of the Hand is a section of the Unknown Regions that consists of an estimated 250 sectors. While many Imperial fluff supporters will be willing to include these 250 sectors into the accounts of the Galactic Empire’s power and resources, I believe it would be fallacious to do so. We know that the EotH only came to the extent of 250 sectors at the point of the novel, which takes place 19 years ABY (after the battle of Yavin). As such it’s resources and material cannot be included into any account of the Galactic Empire – which I will henceforth see as a separate entity. There is also no reason to believe, considering the EotH’s architect (ie Grand Admiral Thrawn), that its defenses would be organized on the same lines as the Galactic Empire’s own sector group fleet order of battle, this due to the fact that it is well recorded that Thrawn was continually given sub-par reinforcements and support from Palpatine – starting his venture with a single Imperial Star Destroyer! There is also the major influence of the Chiss upon the EotH, who accounted for a great percentage of manpower and resources to the creation and continued defense of the EotH. As such, the 250 sectors and their supposed defenses forces will not be taken into the calculations herein. Nor will I include any of the supposed “Deep Core conquests” that Thelea makes allusions to but makes no serious mention of in terms of sources.
There seems to be a distinction between sector groups and fleet assets, perhaps lending some credit to Thelea’s assertion that the Imperial Starfleet and the Imperial Navy are two separate entities. However the size of said assets may vary, as I will try to ascertain below.
According to the WEG “Imperial Sourcebook Second Edition” a system force “is commanded by a systems admiral, also known as a commodore. A system force is responsible for several systems, the admiral being in charge of organizing and coordinating all of his ships throughout a sphere of command spanning hundreds of light years and dozens of worlds, the normal method of communication being no faster than the ships themselves.”
Further, there is the distinction within the WEG material between a Fleet and a System Force. It says clearly that a Fleet is “designated as a ‘sector resource,’ which means it should be available for action anywhere within the sector. A fleet is the smallest unit transferred between sectors. All fleets have a force technical service and force support under their command.” Not only does a Fleet have a different deployment mission but it also has a separate supply and support chain. That is a very clear and indisputable indication of the Imperial Starfleet and Imperial Navy being separate entities – to which System Forces are the building blocks of Starfleet and Fleets are the building blocks of the Imperial Navy. Because the regional forces that would be collected to create the Grand Army of the Republic and from that into the Imperial Military, it is only natural that the organizational structure would remain similar, and as such Imperial Fleets are organized based on a similar structure to system forces, but are not of them. There is also the addendum that certain moffs and grand moffs (such as Tarkin and Carlinson) “could easily have 15 additional squadrons attached to their sector group HQ.” Then there is the last sentence of the Sector Group Organization: “Thousands of Sector Groups are at the Emperor’s command as he seeks to bring the galaxy firmly under his control.”
The differentiation between System Force and Fleet, the fact that moffs could gain “easily” an additional 15 squadrons to their Sector Group HQs (if that’s easy, I wonder how many they could gain through ‘tough’ negotiation), and that it mentions “thousands” of Sector Groups (when there are barely 24 more than a thousand sectors in the known galaxy) it is clear that Thelea was right. But that is not to say that all sector groups were equal (more on that below).
The reason I point out the specification for defining what a system force is, is because of the next sentence: a system force is organized along force pools, available resources categorized by general mission type. While they have a set organization on the OB, a commodore is expected to reform the constituent elements of a pool to tailor the detail to the mission.” Clearly this means that a systems admiral does not have the resources at all times to form every type of System Force (as will be detailed below) but rather he has the constituent parts to make up one or another such system force as the needs of his particular defense and patrol requirements are. His/Her total amount of ships should therefore be calculated as being thus: 3 Imperial Star Destroyers, 6 to 12 torpedo spheres, 30 to 48 cruisers or frigates, 60 to 80 corvettes, 35 to 50 light cruisers, 8 to 16 specially modified recon light cruisers, 4 Evakmark-KDY transport vessels, 4 strike cruisers, 8 FTS Evakmark-KDY transport vessels, 16 Escort Frigates, and 100+ support ships. A System force can therefore muster a (at best) maximum total of 217 warships, 12 torpedo spheres and 112 support ships.
Sector Groups, of which Systems Forces are a constituent part, make up (according to WEG) at least 2,400 ships, 24 of which are Star Destroyers. If we know that each System Force will always contain 3 ISDs, then that means there are roughly 8 System Forces within a single sector, to whit there are: 24 ISDs, 96 torpedo spheres, 1,712 other combat ships and 896 support ships in a single sector group; which means that of the 1,024 sectors in the Galactic Empire, there are an estimated 24,576 ISDs, 98,304 torpedo spheres and 1,753,088 other warships, and 917,594 support ships within the Imperial Starfleet.
In his/her calculations, Commander Thelea included Sector Fleets and System Forces together, which was I think his mistake. Instead of seeing the Sector Fleets and the System Forces as a separate entity, he saw them jointly as being the Imperial Starfleet (aka Coast Guard) and his own estimations of the “25,000 Star Destroyers” comment to be the Imperial Navy (aka the offensive line). He even includes oversectors in this calculations – that being a mistake since Oversectors were not “new” but were rather special political and military zones of authority. No new fleets magically appeared with the creation of the oversectors – it was purely an administrative adjustment to the regional governor decree and allow commanders to cut through red tape.
Now Thelea's argument for the size of the Imperial Fleet/Navy (offensive line) is based on his own observation of Darth Vader's “Death Squadron” (as seen in TESB) and a computer game that mentions a battlecruiser (larger than a standard ISD, but not an SSD) appearing in the aftermath to help chase the Falcon. He then postulates that three ISDs must therefore be an escort for the Executor and the other two must be an escort for the unnamed and only mentioned battlecruiser. However he completely discounts the fact that Death Squadron was a special task force formed by Darth Vader for the sole purpose of hunting down the Rebel Alliance and his son, Luke. In the same way that various Moffs and Grand Moffs had their own personal squadrons that existed outside the normal Order of Battle, Darth Vader as the Commander in Chief of the Imperial Military had his own elite squadron as well. To try and postulate the size of the Imperial Navy based on a misinterpreation of Death Squadron's reason for existence and a single mention in a computer game (of which all such sources are discounted) is reckless to say the least. There is also the dubious figure he states that the Imperial Navy had 25,000 ISDs...but ONLY six – SIX – torpedo spheres. That big of a distribution between capitol ships and siege platforms, especially after he showed how many a Sector's System Forces were suppose to (on paper) maintain is just...it just don't make any sense.
When Thelea talks about Imperial Member World Defense Fleets, he mentions the two Golan II platforms that were defending Coruscant and uses that as the measurement of the rest of the GE. That is a huge mistake in my opinion. It is part of several cannon sources that some systems were better guarded than others. Coruscant, Kuat, and Corellia were all far more heavily guarded that Alderaan, Sluis Van, or Valc III. He also doesn't take into account the various worlds, such as Carida, that might be considered “fortress worlds.” So to assume that all is equal across the board, even at best, would be so absurd as to be a step beyond fallacy.
For example, as he also cites, the Bakuran Defense Forces consisted of a single Carrack-class Cruiser, 6 Corellian Gunships, 3 Marauder-class Corvettes, 5 IR-3F patrol ships, 72 TIE fighters, and 5 TIE bombers. That might be what we can expect from a backwater colony like Bakura, but likely this is not identical to all other colonies. Indeed, in the Poln System of the Candoras Sector (the sector capitol no less) the only Imperial defense forces are four “antiquated” Dreadnought-class Heavy Cruisers and “some smaller ships.” (Choices of One) Clearly there is no cookie-cutter fit to all of the colonies, protectorates, and governorships that existed outside of the official member worlds of the Galactic Empire. And while Thelea stresses that he isn't trying to create a cookie-cutter image, he inevitably does so in trying to form his ultimate calculations.
I personally believe that the number of Torpedo Spheres is exaggerated. It says within the material that there were “at most” 2 Torpedo Spheres within a Torpedo Line, of which a Bombard Squadron was – at paper strength – supposed to have 6 Torp Spheres. Seeing as how most fleet actions were bent around pursuit of rebels and pirates and less about planetary sieges (especially after the end of the Clone Wars and the final stages of the Outer Rim Sieges in the early Imperial years), I am led by sheer military practicality to believe that the number of Torpedo Spheres that the Imperial Military possessed never numbered more than 10,000 at best. Whether some might have been mothballed or otherwise deployed in the roll of orbital stations (removing their mobile ability) is not stated anywhere, but in realistic military sense would make for a better explanation.
Now, for a galaxy-spanning government that has between 1.5 million member worlds, as well as sixty-nine million colonies, protectorates and puppet states (Essential Atlas), to as many as (according to the new Fantasy Flight Games “Edge of the Empire RPG Core Rulebook) “1.75 million planets [that] are fully represented and integrated into the Galactic Empire” this military seems small. That alone means that each individual ISD would be, in some aspect or another, responsible for protecting and policing 61 inhabited worlds. Even with the additional warships (cruisers, frigates, corvettes, and smaller) there would barely be 1.1 ship per planet. As such, I believe that these numbers give credence to the idea that the Imperial Starfleet is a type of “Coast Guard” or purely Self-Defense & Policing Force, whereas the Imperial Navy is the actual fighting crème-la-crème of the Imperial military and represents its offensive capability.
It is quite easy, considering the Galactic Empire’ size, political foundation, and strong economy that it could produce twice the number of estimated ISDs and bring about a total number of at least 50,000 ISDs – half used for Sector defense and police work, and half used for offensive and cross-sector-border pursuits.
Now, concerning Star Destroyers, we have to realize that the Galactic Empire built its military up from the already considerable size of the Grand Army of the Republic. It is a stone-cold fact that the Republic ordered and received over a thousand Acclamator-class Assault Ships (early prototype to the later wedge-shaped ships) and thousands of sub-classes to that design. They also built and received thousands of Venator-class Star Destroyers. In the movies and the Essential guides it is made clear that almost a thousand Venator-class SDs took part in the Battle of Coruscant where General Grevious made his bid to capture Palpatine – a thousand! All while the Republic was on the frontiers fighting with 20 “sector armies” that spanned across distances that can only be described as friggen' gargantuan, what we'd consider to be dozens of normal regional sectors. You could probably argue that these Republic Army Sectors were the inspiration for Tarkin's “special oversectors.” Otherwise, if you try to take it at face value, you get into the minimilization craze brought on by Karen Travis (let's not have that argument again, shall we?). So clearly, we have thousands, possible tens of thousands, of Acclamators, Venators and even the eventual rise of the Victory-class Star Destroyers, all ready for use by the Galactic Empire.
There is no indication by either the WEG, FFG, or Essential guides that the Imperial Military made a marked distinction between the various classes and subclasses of Star Destroyers. So when I say that there were at least 50,000 Star Destroyers, it's quite possible that a 5th of them are older models and such.
Long story short, of the 1,024 sectors in the Galactic Empire, there are an estimated 24,576 Star Destroyers, 98,304 torpedo spheres and 1,753,088 other warships, and 917,594 support ships within the Imperial Starfleet. (Coast Guard)
The Imperial Navy (offensive line) is another matter. Seeing as its late for me, I'll do those calculations tomorrow and make a second post. I've already explained my position in support of and opposition of Thelea's assessment and here with my own. It does not take into account the local defense forces and privately raised (non-Imperial) forces that planets that are aligned with the Galactic Empire, but left to their own defense issues, may or may not have. This is solely for the Imperial Starfleet and Navy.
Spoiler