What is a large capacity transport where:
(a) the cost of carried units are comparable to the transport?
(b) the cost of units capable of killing the transport are comparable to the cost of transport?
After fiddling with this optimization for awhile, the Warmother (below) popped out. Any oversights here?
The heavy transport style of military dropship does not seem to exist in canon, but I'll argue it
should. The ability to travel by jumpship implies the ability to create jump circuits, which in turn implies the ability to project force by (perhaps) 360 light years/day through a hop on the circuit every 2 hours. If that rapid deployment force can be made sufficiently powerful, it can strongly define a star nations defense ability. Minor border incursions could be met with heavy force before they manage to secure a planet, and even a major multi-planet invasion becomes much more problematic to plan and staff when a powerful defensive force can be rapidly deployed at any one of those planets.
Projecting force via jump circuit creates a strong necessity to maximize the amount of force per jump collar because the cost of a jump collar is ~200M, implying that the cost of a jump circuit is ~200M/30 light years/collar. Hence, a jump circuit 12 jumps long costs ~2.4B/collar. In that context sticking a Union (2174.5 tons of transport) or even an Overlord (6350 tons of transport) on the jump circuit seems like quite a waste in comparison to the Warmother, which can transport about 3x more at a fully loaded cost which amortizes the jump circuit collar.
The big drawback of a heavy transport is the 'all eggs in one basket' effect---losing the transport is catastrophic. This is why question (b) was an important design criteria. Having a transport which need not touch down on the planetary surface aids this substantially, since you don't need to worry about overrun by enemy ground units, artillery, or
suicidal VTOLs. This could be done with an ASF force, although options exist (see below) for something more comprehensive.
The next step notes that the most effective way to increase the cost of destruction is by increasing thrust, so only fast units can run down and attack the Warmother. At a 7/11 speed, even medium ASF will struggle to reach the Warmother due to the risk of structural damage. Instead, you really need something along the lines of the
Piranha assault smallcraft which seem to dominate assault dropships / pocket warships in a cost vs. force tradeoff.
At that point, whether or not the Warmother survives comes down to a question of armor and firepower. Keeping the cost of the Warmother low is important here, so the primary source of firepower is provided by transported Aerospace fighters. Optimizing this tradeoff, you end up at an intuitive optimum of heavy armor, and the unintuitive optimum of 49.9k tons. Any larger implies the inefficiency of armor on large dropships becomes significantly more prominent, while at any smaller scale you fail to really leverage the transport possibilities of a jump collar.
Once we've established the desirability and feasibility of a heavy transport, it's important to ask: What should it transport to be effective? There is a strong case for a pure ASF carrier since that would maximize the feasibility of paralyzing enemy transport in and out of a system. This however is unsatisfactory as watching friendly ground forces be overrun is an unpleasant thought. The ability for carried units to switch hit between space and ground ops like the
Workhorse ASF and
Marine Battle Armor suggests an alternative: I've configured the transport bays for the
IS Triad force which is about about a lance scale, implying the 20 transported triads are regimental in strength. Formally, it's a regiment of ASF, a battalion of battle armor, and a regiment of
light VTOLs.
These are supported triads with an
M^3 smallcraft making them capable of deploying independently for extended operations to multiple locations across a planet as the situation merits. The Warmother has the necessary cargo to fully support each triad as detailed
here, providing supplies to support multiple combats that are high speed, space, ground, or boarding operations. Steerage quarters are provided for all techs and bay personnel enabling long endurance missions up to 150 days, and there is ample tech support for maintenance and repair.
What other missions can it easily satisfy? Investing in steerage quarters for all passengers enables massed use in offensive deployments while reducing the misery of techs-in-infantry-bays. Offensive deployments (somewhat ironically) naturally take longer, since they may not involve deployment by jump circuit. This also creates quite a bit of spare capacity for extra passengers, should that be necessary. The extra cargo capacity can of course be used in many different ways. In essence, this is the opposite of the Overlord philosophy of shaving down to almost no cargo. There is some cost here---if cargo capacity was used in the Overlord philosophy and we eliminated steerage quarters, we could transport somewhat more triads, but they would only be able to handle one of ground or space combat, not either and both as needed, and mission endurance would be reduced to one significant battle rather than the ability to potentially sustain over many. Overall, the multi-use nature here seems like a plausibly better call, at least in a context where there's only one heavy transport design in use.
Warmother
Type: Military Spheriod
Mass: 49,900 tons
Technology Base: Inner Sphere (Standard)
Introduced: 3145
Mass: 49,900
Battle Value: 8,687
Tech Rating/Availability: E/X-X-X-D
Cost: 1,371,020,000 C-bills
Fuel: 1,000 tons (10,000) //680 tons is a reserve for the Triads. 320 is for the Warmother
Safe Thrust: 7
Maximum Thrust: 11
Heat Sinks: 392 (784)
Structural Integrity: 60
Armor
Nose: 730
Sides: 729/729
Aft: 730
Cargo
Bay 1: Small Craft (20) 2 Doors
Bay 2: Fighter (40) 5 Doors
Bay 3: Cargo (4033.5 tons) 1 Door //3320 is standard IS Triad supplies, 285 is standard Warmother supplies, 428.5 is general purpose.
Ammunition:
4,752 rounds of Anti-Missile System [IS] ammunition (396 tons)
Escape Pods: 69
Life Boats: 69
Crew: 3 officers, 11 enlisted/non-rated, 1 gunner, 180 bay personnel, 780 passengers, 32 BA marines
Notes: Mounts 216 tons of heavy ferro-aluminum armor.
Weapons: Capital Attack Values (Standard)
Arc (Heat) Heat SRV MRV LRV ERV Class
Nose (17 Heat)
2 Anti-Missile System 2 1(6) 0(0) 0(0) 0(0) AMS
Anti-Missile System Ammo [IS] (792 shots)
1 ER PPC 15 1(10) 1(10) 1(10) 0(0) PPC
RS/LS Fwd (2 Heat)
2 Anti-Missile System 2 1(6) 0(0) 0(0) 0(0) AMS
Anti-Missile System Ammo [IS] (792 shots)
RS/LS Aft (17 Heat)
2 Anti-Missile System 2 1(6) 0(0) 0(0) 0(0) AMS
Anti-Missile System Ammo [IS] (792 shots)
1 ER PPC 15 1(10) 1(10) 1(10) 0(0) PPC
Aft (2 Heat)
2 Anti-Missile System 2 1(6) 0(0) 0(0) 0(0) AMS
Anti-Missile System Ammo [IS] (792 shots)
A fully loaded Warmother costs 2158M including all triads with their supplies as well as spare parts and consumables for 5 months. Viewed another way, this is 108M/Triad.
Edit: Updated by reducing to 20 IS triads to provide more space for cargo supplies. Also added full Lifeboat/Escape Pod capacity.