It's a fact that you go to war with the space fleet you have. As I said in the previous post building big ships is uneconomical. Smaller ships can cover more bases and provide more surface area for mounting weapon systems.
The Republic of Alpha and their neighbors, the Evil Empire of Beta are beginning hostilities. More than likely the first blow in any war will be crucial. Going off unprepared will be worse than doing nothing at all as it will waste ships and leave one open to attack.
The Empire started out as a trade-friendly province in the mod rim. They were a local cluster capital and they produced mid-range (200 meter) ships for the Old Empire Navy. Since the Old Empire fell and a plethora of new empires (note the capitalization conventions) Beta decided to follow suit. After all, the new golden age has to start somewhere.
They could build the biggest ships, but most of their worlds are agrarian with bucolic and stupid locals who do not build let alone comprehend the problems of building and crewing starships. Pilots, engineers and trained crew are crucial. The shipyards were optimized for such ships. It was their role in the galactic economy (RIP) and were less than efficient at building smaller ships. Furthermore, the firms producing larger ship systems were all tight with the Evil Parliament and you didn't want to mess with them.
The Alpha Polity was a frontier province. It had shipyard facilities to service the smaller navy vessels and with some corner cutting can now produce smaller (100 meter) ships. Being spread out with defense and research outposts they have a larger pool of crew than the Betans but can't produce such big beautiful ships. The square cube law says the Betans are doomed. What can reverse this? Evil empires are a necessary component of the dramatic tension constant! Without the DTC the universe just ... winds ... down ... Everyone stays home and shops for shoes or hats.
First, realize that people in power want to remain in power. Good guys and bad guys have that in common. Betans have a number of strategies to boost their firepower:
1) Alliance with a power that will enhance their strengths and minimize their weaknesses. In this case someone with smaller vessels. this might be hard due to the 'Evil' in their title but it's too late to change the letterheads!
2) A comprehensive education program for the bucolic population. That will take years and who wants to SF RPGs about comprehensive education reform? Monte Cook couldn't sell that idea.
3) Go with the ship numbers and crew numbers they have. Once the Alpha Polity is conquered we will use their shipyards and non-bucolic population to increase our forces!!!
Going with the plans for a brief successful campaign against the Alphans means maximizing the effectiveness of the Betan warships.
The first design proposal was to simply stack eight 100 meter hulls lengthwise. this would have very nearly the surface area to equal eight Alphan ships in surface area. that was shot down (pun intended) quickly. A ship that long and skinny would have insufficient area to mount enough thrusters aft. The length made maneuvering harder and the shape was comparatively fragile.
The next design proposal was to make most of the weapon systems internal. There were several ways to do this. The first was the spinal mount, building the ship around a horrifically huge weapon. This worked quite well if your target wasn't moving. Otherwise you had to steer the whole bloody ship.
Then next three proposals were simple: missiles, missiles, MISSILES!
While missile launchers took up space on a hull, they required ammunition which required volume. This was the main reason energy weapons were often favored over missiles. You could fire those till your power plant gave out. Larger ships could carry more missiles and afford to fire more missiles at longer ranges. More missiles co uld overwhelm defenses. Thus if you were lucky you could cripple or destroy several smaller ships.
This had application for commerce raiding. Instead of say, five defending gunboats of 100 meters to tackle a raider, you'd need six or seven since several would be disabled by long range fire before coming to grips. These extra ships added ip fast when you were dispatching several task forces to find such a raider.
As the Alphans soon learned such larger ships could also lay eight times more mines, creating a hazard for civilian shipping that required military ships to clear.
The Evil Empire of Beta was also open to commerce raiding of course. However, the Alphan ships also had less fuel and supplies and thus a shorter range. The Evil Overlords gladly allowed several worlds of their frontier to be cut off. Remember the part about the high technology assets being concentrated on their capital?
In any case when the raiding an feinting was over a tad force of 20 Alphan ships faced an incursion of four Betan cruisers. Only the invaders were content to lob a whole bunch of missiles at long range, watch a few score telling blows and leave. They would repeat the process in a war of attrition. Appear, fire off long ranged missiles and leave.
While this went on the Betans and Alphans were desperately trying to build more ships to tip the balance of power. Ironically the fleet with the larger ships continued hit and run and raiding tactics. The fleet of smaller gunboats would try to maneuver their enemy into a telling battle because losing even one such cruiser would be a huge loss.