1920s future fleets

[TacCovert4]

I see MTBs primarily as coast defense, and not suited to all sea areas.

So far, in wars, I've put limitations on them operating based on the sea state the weather chart comes up with.

They won't be based in large numbers in say Cape Town, as those seas
are rough.

Sumatra though- much better.  Sheltered waters, and lots and lots
of rivers they can go hide in out of 'reach' of any foes.
Same with say the Limpopo delta, or defending Ria de Janerio bay,
digging them out of the nooks and crannies will be problematic.
Far more than an equivalent tonnage of light destroyers.

I don't necessarily see throwing them at a main fleet as the best use.
Sending them after supply efforts, beachheads, bombardment squadrons, and interdicting
local merchant traffic is the prime role.

As for the main force .... It's an option - and could be done, but pretty much destroys your MTB force.
That said, I think that about destroyer forces doing attacks as well.
Destroyers are far better rounded and seafaring, but are very fragile.

Both can be useful, but need to be used situationally.
If I'm going to do a main force attack, I'd want to tie it to a separate effort - like the arrival
of a main fleet force, so that I can take advantage of the disruption and damaged units.
Alternately flip it and use the MTBs as follow up to a raid that draws forces away from
an amphibious force.

Peacetime, as I said, I see a use for many light patrol platforms for simple patrol of extensive
coasts and getting into the shallows.

Long term choices, I'm looking that I can build 16 MTBs for the cost of a light DD (640t)
There are - to me- many cases where the 16 tiny hulls have more value than the 1 hull.
more torpedo platforms,  and take 16 shell hits vs. basically 1.

Roughly speaking that's my philosophy as well.

MTBs are harassment forces, a torpedo force in being for island bases and other small places.  They require someone to defend everywhere with more than a single ship, as a score of MTBs can bumrush and sink even a battleship that's caught without support. 

GTBs are what I went for as a 'fleet' torpedo asset.  Better seakeeping, actual comms (for 1913, in '23 and later 40t MTBs would start having reliable short-range comms), and fire control.  They're a 'night attack' force.  Whereas an MTB might be slinging an 18in torpedo at suicide ranges of 3000yds.....a GTB can sling a heavyweight 21in torpedo at 8,000yds.  The former will always be spotted.  The latter, being low slung and operating at night or in weather, MIGHT not be spotted.  And due to the range difference, the former can be targeted by basically anything bigger than an MG on a ship....the latter is going to be in the envelope for 100mm and larger guns, which reduces the number of things that CAN threaten them.

IF I had to fight Rome again in 1918, which wasn't an impossibility at one point, my plan was to do a night attack with cruisers and DDs providing overwatch for GTB squadrons rolling in and launching waves of torpedoes at longer ranges to disrupt and shape the battle (if a larger fleet battle is in the offing) or cause significant damage/losses.  If the fight was to continue at night, in a lesson learned from Ironclad Bay, the MTBs would have a GTB 'Squadron Leader' that would go in with them to the 'initial point' where the attack run is to begin....thus precluding the cluster-frag that happened at Ironclad Bay where poor communication meant the MTBs went in on a poor angle and poor timing and disrupted other friendly operations rather than the devastating flank strike they could have done.  DDs, which would have been gun dueling with the enemy screen at range (keeping the battle line out of the gun duel) would go in last to pick off crippled ships, same with the cruisers.

[Kaiser Kirk]

The Pesh-kabr or Sea Hornet 500ton coastal destroyers are meant to fill that GTB role Tac's talking about. 
as well as the open sea patrol, in affordable squadrons.

In the event, I may go with updated 750 ton vessels, but that entire construction
program seems like a '24-25 time frame if I can fit it in.

[TacCovert4]

The Pesh-kabr or Sea Hornet 500ton coastal destroyers are meant to fill that GTB role Tac's talking about. 
as well as the open sea patrol, in affordable squadrons.

In the event, I may go with updated 750 ton vessels, but that entire construction
program seems like a '24-25 time frame if I can fit it in.

My GTBs are only 10 years old, so they're not quite obsolete yet.  I'm probably going to hold out for another 2-3 years before I build another GTB run. 

Currently the H-class General Purpose destroyers, slow'ish but with a modestly adequate armament, torpedoes, and most importantly good ASW gear are the major production run.  I-class Destroyer Leaders as well.