Setting info - take it as granted. Strategy - treat it as an open issue, if you see an alternative solution, please suggest it. Setting - natural conditions Planet to defend - Earthlike, tidal locked around red dwarf, water world, cold, 3 atm Main weakness point - gates - that allow teleportation between worlds, indestructible (but all area nearby can be ex. mined) Setting - social/political conditions Technology - not much better than early XXI century, except weak AIs (like self driving cars), mostly tech stagnation, jets and nuclear technology exists only in archives (if necessary it would be possible to recreate them but cost would be too high) Population a bit less than 10 mln Political system involve mixture democracy, technocracy and Brave New World totalitarianism. (the only setting where population freely voice its outrage concerning Big Brother system cost overruns... no, it's not fully sane place...) Assets - well educated masses, low corruption, effective state, industrial base, surveillance systems, plenty of time for preparation and testing. Weakness - because of lack of known enemies, there would be an awful pressure to keep military expenditure really low; no real enemy means that the equipment or tactics is not tested in combat conditions. Setting - main points worth defending Main city and surrounding area (over 90% of population) Mines / dams spread all over planet Transport routes (mostly sea / river) and electricity lines Setting - potential invader - unknown -there may be even more crazy group that survived and dream about conquest -there may be also some refugees / explorers / diplomats trying to cross gates, so shooting without asking question would be unwise Strategy -keep microscopic standing army, invest most of money in building huge supplies of weapons (just in case rely on conscripts) -hide those weapons underground, to avoid easy targetting -use passive multistatic radar arrays (hard to detect, don't use much electricity) -give up any idea of fighter jets, just invest in SAMs (yes, poor man way of denying one air superiority) and medium range A2A missiles -use production lines for civilian equipment for dual use (like only slightly modifying civilian planes or using the same chassis both for tanks and bulldozers) -make all drones cheap (simple design, standardized, cheap materials, long series), with intention to beat any enemy with Zerg rush tactics -continue production in spite of having huge reserves in order not to lose expertise (yes, it would lead to huge armies in long run) -get a few standardized weapons and use it for all purposes (so one heavy cannon for tanks, ships, fortresses, etc) -use mobile phones electronics to create cheap smart bombs -encircle all gates with barbed wire and wide minefields, make un-mined exit routes with auto-turrets -near each mine/dam put an airport ( both for evacuating staff and for being able to use it for bombardment) -surround all valuable objects with heavy fortifications, bunkers, mine fields, turrets, etc. In case of the capitol - with multiple lines -spread in random places some SAM, or anti air machine gun turret -invest in high redundancy of electricity grid to prevent easy destructions -put redundant communication cables between bases, in case of destruction use expendable balloons (like those of google) for communication grid -using mobile phone net to get a cheap equivalent of GPS system -make aircrafta able to refuel in air to be able to fight a war on the other side of the planet -send on a front line a cheap army of drones first, something in this price range, but armed with a few cheap rockets: https://en.wikipedia.org/wiki/Dova_DV-1_Skylark (it cost 1.5 Stinger, so using anything more expensive than Stinger to shoot it down may be a bad business) -stockpile insane reserves of materials, like fuel, spread it around (this can be justified to society as precaution for natural disaster) -make tiny quadcopters armed with modified pistols - in huge quantities and use to fight enemy infantry. Separately a caring copter and an armed immobile "egg" armed with gun. Everything fed with base ships where "birds" can replace batteries. Sell the same (unarmed) drones to public to provide them with fun and recoup part of R&D cost. -use small (one metre tall) drones on chassis armed pending on variant with machine gun / small cannon / rockets mortar. -standard terrain car with rockets turned in to something like more mobile and more precise Katyusha (an expendable nightmare for enemy tanks) -provide citizens with very realistic computer games where they may be leading a squad of drones. Make a competition, fund a cup and keep in database who can do it well... -as last resort have stockpiles of guns to be handed to all citizens to make a last stand in capitol (mostly to have last argument while suing for peace) Suggestions concerning strategy? Would you prepare differently under such conditions?