I think sub-like designs have a clear niche if you have an undetected dormant jump point entrance into an enemy system, or if you're encountering the enemy in 'neutral' systems, but they have no real way to sneak past guarded jump points, so you often wouldn't be able to make use of them at all when advancing into enemy territory. I think there are a few roles where a sub-like design would be useful, though:
- The classic commerce raider role - give a small ship with a cloaking device & low-powered thermal-signature-reduced engine a handful of very large slow-loading missile launchers, design some long-range two-stage missiles with ECM and huge ship-killing warheads to fit them, give them active sensors tuned to enemy commercial ship sizes, keep your sensor and MFC off until you find a thermal contact, turn them back off after your missiles hit and reposition using your stealth to avoid active sensors, have a 'sub tender' on the other side of the dormant JP with an appropriate-sized jump drive to let your subs transit, plus colliers/tankers/maintenance ships. . . I think you could build a semi-practical commerce raider at about 3000t, which is the maximum size a military ship can be to use the smallest-sized jump tender you can build with the earliest jump tech, which is pretty small and cheap for something that could kill a commercial ship many times its size
- 'Boomers' - you can target colonies using waypoints, so you can launch missiles at them from any point in a system even with a tiny MFC and no active sensor, which means you could hide a large and slow but stealthy long-deployment ship full of big box launchers with long-range colony-killing missiles far out beyond the outer reaches of a system and threaten any inadequately-protected colony with impunity, probably a good thing to sneak these into systems of NPRs you're currently neutral with when relations start getting bad so you can respond to the start of hostilities with a massive alpha strike
- Spy subs - use ELINT modules instead of missiles
- Special operations subs - stealthy dropships that can land company-sized units of marine commandos on poorly defended colonies without warning
- Fleet subs - ships that are stealthy but still fast enough to keep up with a battle fleet, can be used as scouts and sensor pickets
- Minelayers - I heard mines are bugged at the moment but minelayers can still be useful by dropping sensor buoys, stealth will let them do it safely closer to the enemy where they'd be useful
- Fighter tender - give a small cloaked ship boat bays and some extra supplies instead of missiles so they can resupply fighters while hiding in enemy-held systems, one of these could tend a large number of stealth scout fighters
The commerce raider role could even use active sensor missiles which would allow it to turn off its actives immediately after firing
Can one fire missiles with their actives sensors, to way points, then have the one reaching the way point, begin targeting what ever they find?
So if you Submarine detected Thermal signatures at a Gas Giant and assumed it was a Fuel refining operation, WP it and fire off missiles to the way point, without having to turn on its own Active Sensors
