An empire's Fleet Supply limits the number of ships that it can control at any one time. Each ship costs a certain number of supply points. Refer to the list of Ship Types for the exact supply cost of each ship design. In order to raise your supply point total, an empire must Research additional levels of Global Fleet Supply under the Fleet Logistics research section.
Global Fleet Supply
At the beginning of every game, empires start with one hundred available fleet supply. Global fleet supply is increased by completing research in the supply tree under the Fleet Logistics section of research. All ships other than strikecraft require fleet supply to operate. The amount of supply required by a ship varies significantly depending on the ship.
Each level of research completed allows an empire to sustain more ships. In addition to this, each level of research imposes a permanent drain on an empire's total income. Later upgrades are more significant than earlier upgrades.
In Diplomacy, TEC can establish a Supply Pact with one ally. This pact is unlocked through the top-level upgrade in TEC's Diplomacy Tree, requiring 8 Civics Labs. It requires relationship of 18.0 and reduces fleet supply upkeep costs by 15% and increases fleet supply by 100.
Fleet Size Setting
When starting a game, fleets can be set to Small, Normal, and Large size in the pre-start settings screen. This does not influence ships' supply costs or the number of capital ships available per level of the Command research tree. Rather, the fleet size setting changes the amount of fleet supply available per level of the Supply tree (without affecting upkeep costs per level). Small Fleets decreases fleet supply at all levels by 25%, while Large Fleets increases it by the same amount. Note however that the Fleet Supply research mouse-over tooltips will still show the supply sizes from Normal Fleets even if you are using a different setting -- meaning that if you are not playing with Normal Fleets, the only way you can see your total available fleet supply is in the 'Current Supply' -- 'Next Supply' window directly above the supply research tree.
Follows a table of fleet supply available by level and fleet size setting:
Fleet supply by fleet size setting
Impact on game mechanics
The fleet size setting has a rather pronounced effect on gameplay: Even though you are not allowed to build any more or less capital ships with a different fleet size setting, you can afford to sustain a larger/smaller fleet at the same level of supply -- and thus, upkeep costs. This changes game dynamics, especially in early game and early mid-game to mid-game, because the drain on resources represented by fleet supply has a large impact on the development speed of your empire at these times.
In late mid-game and late game, your empire is generally fairly large and mature and most research (that you want) has been done, leading to a markedly different income-expenditure balance -- essentially, you generate much more excess resources than earlier in the game. Regardless of whether or not that is enough for what you need to purchase, your budget constraints are much looser; that means an additional level of fleet supply (and thus, upkeep) will not, relatively speaking, tax your economy nearly as much later on in the game as it does in the earlier stages. Perhaps most important is the corrolary of this state of affairs that an extra level of upkeep early in the game will considerably delay your reaching the point where you can more easily afford that upkeep; this effect obviously gradually fades in strength as your game progresses, until you reach (in simplified terms) the economic "turnover point" where you start generating enough excess resources that an extra level of upkeep will not appreciably hinder your development in other areas.
That is why the fleet size setting radically changes the economic dynamics of the game's earlier phases: Assuming Normal Fleets as the baseline, with Large Fleets you can afford a considerably more powerful fleet on a given level of upkeep; most significanty, you can afford more capital ships. It is true that a larger fleet still costs more to build, but even with Large Fleets the fleet sizes you can sustain at the first few levels of upkeep are not so huge as for the direct purchase cost of the units to make a noteworthy difference in your overall empire development strategy: It is the upkeep that constitutes the real price of fleet buildup.
Conversely, with Small Fleets you will probably be forced to accept larger upkeep in order to be able to pursue an effective military strategy -- if nothing else, the planetary defense forces (militia) are still the same size no matter what Fleet Size is set to, meaning that there still is a minimum force level you must commit to clearing unoccupied planets of the militias -- either that, or you can make up for the force difference by micromanaging your conquest fleets. This can usually improve their efficiency considerably (depending on your skill and experience with the game), but skilled or not, it still costs you time in the real world which you cannot spend developing other aspects of your empire.
Regardless of what Fleet Size is set to, the setting is binding for all players in the game, meaning all your opponents (or allies) will face the same situation as yourself. That means none of the settings gives an actual advantage in the game to you or your opposition -- although it is quite possible that a particuar setting will suit your preferred play style better. In particular, Large Fleets tends to make the earlier phases of the game more dynamic and partially shifts the balance of game focus from economics to combat: Put simply, one of the main constraints on economic growth -- upkeep -- is looser, meaning you can spend less time worrying about the economy to achieve the same level of play efficiency; on the other hand, you and everyone else can build large fleets faster (even if you are constrained in your shibuilding efforts by resource availability, the lower upkeep burden gives you, relatively speaking, more resources to work with), meaning that you are likely to find yourself clashing with other factions more often and with larger forces.
By contrast, Small Fleets makes the economic constraints necessitated by your military power more acute, meaning that you (and the others) cannot afford fleets as large and you must give more attention to your economic development if you hope to compensate for the increased burden of retaining your military. Neither of these options makes the game more or less difficult; it simply makes the pace (and game priorities) somewhat different. Also, in general it may be said that the higher your fleet size setting, the shorter the early phases of the game are, both absolutely and relative to total play time (even though larger fleets also tends to mean the game is somewhat shorter overall, but the play time reduction is due to the shorter early phases; later phases are generally not noticeably affected either way).
Even though difficulty is in principle not really affected by Fleet Size, it can still be said that against opponents who are less efficient at managing and developing their economy, larger fleets make the game easier ('efficient' meaning essentially how fast your empire grows stronger in resource gathering and research, no matter what the starting position for this observation is). This is because the advantage that you enjoy over your opponent because of your superior efficiency at game economics is magnified by player ecnonomies being less constrained in their development (the military power balance between you and your opponents is essentially unaffected by fleet sizes, as your relative maximum fleet sizes at given upkeep remain the same, which means that only the economic side of gameplay can generate an advantage from fleet size setting changes).
If, on the other hand, your opponent is economically more efficient than you, he will enjoy that same kind of magnified advantage over you, making the game harder with larger fleets. Neither of these cases would necessarily apply if you are playing in teams and your teammates have a different level of economic efficiency than you do, as then your advantage or disadvantage may be diluted by your allies' respective levels of economic aptitude; in team games, the determining factor for the relative advantage stemming from the fleet size setting would be the relative combined (more precisely, averaged with weighting by economy size relative to rest of team) economic efficiency of the teams.
To give an example, a game against low-difficulty computer opponents will probably be easier with larger fleets, as the computer at low difficulty is generally a poorer economic administrator than most players (the exact level where your and the computer's skills at economic management equalize depends on your skill, but the default Normal difficulty computer player is typically poorer at overall economic development efficiency than even a moderately skilled human player, even when the computer player is set to the 'economist' play-style).
Capital Ship Supply
At the beginning of every game, empires start with one available capital ship crew. All capital ships require one capital ship crew and 50 fleet capacity. A Titan takes up 2 Capital Ship crews as well as 150 Fleet Supply. The number of available capital ship crews is increased by completing research in the command tree under the Fleet Logistics section of research.
Each level of research completed allows an empire to command more capital ships. Later upgrades are more significant than earlier upgrades.
Note that unlike Fleet Supply, Capital Ship supply does not affect fleet upkeep.
Fleet Supply Amounts by Ship
Titans are all 150 supply.
Capital ships all are 50 Supply.