Ok, I had a look around. No Civil Defenses anywhere in sight
(), in many cases not even a Barracks for rapid healing after an onslaught, but that's less important for now.
The Meeting Room, The Pier and The Bayou are all metropoleis. They give +100% defense bonus to the units stationed there. With a radar tower and fortification, that's another 50% for 150% total. The same goes for any units stationed on one of the two mountains, assuming a radar tower close by, which we obviously will have. It also goes for The Shallows, being on a hill with walls.
The New Yard, The Marina, The Red Tape and The Squeeze are cities, for a total of 100% bonus to defense. The same goes for any units stationed on a hill up in the north around The Shallows, as well as The Greenhouse with walls.
The Hideaway has 75% with walls and fortify, The Whalepond only 25%, which also goes for if we disband those towns and leave units there.
The probability that a vet Marine kills a vet MA that has 150% bonus is ~5.2% (using Offa's calculator here). The probability that 12 Marines kill 2 Mechs and 4 MAs is <0.1% (~0.06% if it matters). It's still <0.1 for 1 Mech and 5 MAs.
With 100% defense bonus, the probability that 12 Marines kill 2 Mechs and 5 MAs is <0.1% (~0.05%). 1 Mech and 6 MAs would do too, even 7 MAs is <0.1%
With 75% defense bonus, the probability that 12 Marines kill 6 Mechs is ~0.6%. We could save The Hideaway that way.
With 25% defense bonus, the probability that 12 Marines kill 4 Mechs is slightly less than 50%. I find it very unlikely SABER would try their whole stack of Marines taking one of the islands under those circumstances, if we disband the towns. And if they do - we'll be the ones dancing with joy.
We have two mountain tiles and 3 metropoleis that together need 5 Mechs and 25 MAs. We could include The Shallows too, making it 6 Mechs and 30 MAs. Make that 8 Mechs and 30 MAs, we want some extra in The Shallows if we are to keep it and not disband.
We have 4 Cities and 4 hills (5 if we disband The Shallows, but I'm counting that above) that together need 8 Mechs and 48 MAs. That's 16 Mechs and 78 MAs total. We don't have that many MAs, but a regular Mech is almost equivalent, in particular if it's at the bottom of the stack.
On top of this, we could add 6 Mechs to The Hideaway and 4 Mechs to the disbanded The Whale Pond. Some of these could be regulars, no big deal.
Total: 26 Mechs and 78 MAs. Since we don't have that many MAs, make that 31 Mechs and 73 MAs, which is exactly what we have on the mainland or headed there from SCI. The SAMs and Marines are only bonuses.
Oh, and this means we should definitely sink that Carrier, if we can.
Note that I haven't calculated with bombardment here, but if we take down that Carrier and a few of the surface ships, there isn't much of that to go around. And with the SAMs that we could portion out, we shouldn't need to worry too much about that.
. The island cities don't actually benefit us all that much really, but they do give Saber the chance of using to use them as cover for their boats, and they could land a bunch of artis/bomber on them if we kept the cities.
