I suspect that they would have to go with the Swiss model. Rifle in every home, every male required to receive military training. Could be set up and executed within a couple of years. Hard to do overnight but very effective to prevent the country from being attacked.
They could make it compulsory as part of the education system. Similar to our JROTC program in High School. Learn to march, basic military ranks, general orders, basic first aid, basic military squad level tactics and basic rifle marksmanship in a 1 school year program.
BTW, this is something that I think we should be doing.
OMG - no chance.