In the case of Vietnam, nothing was gained against North Vietnam in ten years of expensive combat ... just stalemate. Of course, here the real question was "How do you overthrow a smaller country which you can utterly obliterate in 15 minutes?". The answer was never found (nor were the Russians able to figure it out in Afganistan).
In the case of Cuba, we have a fairly easy target. It's population is much smaller than Vietnam so that attrition would grind them down in maybe two years of fighting, i.e. they wouldn't be able to replace the dead soldiers as fast as they were killed.
But if killing soldiers is the most cost effective way to knock off another government I wouldn't be typing this out ... would I?
In fact, the best way to get rid of the thing is a combination of imagination with a bit of force. I mean ...
The first thing to do (given that you don't want to throw American lives away) is to establish how much money you are willing to spend on the project. I think it would be worth $5 billion to get rid of this "problem". Some might think less ... others more. This is just a hypothetical figure anyway.
Now, how many new homes could you buy? ... new cars ... new TVs ... new computers nowadays ... just "stuff" that people want. We're gonna' give it away to the Cuban people in the "Freedom Lottery". Just drop the lottery tickets on their heads one day from the air (the Cuban air farce couldn't stop it). Here's your ticket.
Now on the other side (this could be a fold out thingy too cause we may need more space ... or tear off ticket at dotted line).
We need to list the winnings which are possible, i.e. how many new homes and something about square footage, etc. , how many TVs & cars ... blah, blah, blah. Some pics would go over well also.
A description of their new government, its benefits, etc. and a detailed list of formal philosophical reasons for dumping the present system are required. For moral support, you might send individualized messages from American families encouraging them to ... fight for what's right!
Now, we also need to give a "bounty" for military hardware captured & turned in or just eliminated. Like "Earn $250,000 cash for a tank" ... "$100,000 for a helicopter" ... "$300,000 for a gunboat".
There is a statement in "The Art of War" ... "Always give your enemy a way out". The reason for this is that the enemy will not fight as hard if he knows that there is an alternative other than death. So we want to give the army commanders a way out ... from a life threatening situation to a "beachfront retirement" by employing the simple expedient of turning himself in for the bounty. Remember, our goal here is to displace the tyrant ... not kill people (even if they deserve killing). Therefore ...
$20,000,000 for Castro (live) $10,000,000 (dead)
These lists should be as specific as possible, detailed, with directions on how to proceed after the "war" is won. The "brochure" should be in Spanish of course and very upbeat ... like real advertising.
You need a date now.
When is this to take place? No one is going to go out and risk his life not knowing if others around him will back up his rebellion. One of the main reasons that a culture can be enslaved over long periods by a small percentage of its people is the lack of communication and the impossibility of coordinated attack.
In every possible way this is to be decided beforehand for them in the advertising brochure.
After the "AD drop" comes the "Gun drop" ... individually parachuted, loaded, ready to rock, rifles. Decent effective ones. And other anti-personnel hardware, i.e. hand grenades, etc. These gun drops go on every day for many weeks to ensure that many people who want them have the "tools" of meaningful rebellion.
They should be directed to capture-kill immediately the lower echelon of government. They won't be able to get to the higher but the lower always has its butt hanging out. Removing the lower echelon worked to great effect in Solzhenitzen's Gulag Archipelago ... it should work anywhere. This will serve, in connection with the next ingredient, to break the back of the incumbent resistance.
Now ... the kicker.
The USA promises in the brochure that if the rebellion begins in earnest ... it will weigh in militarily to support and ensure the success of the enterprise. It must say so in no uncertain terms that come what may ... the thing will succeed. With all the foregoing in place ... Castro is history with the minimal loss of life and least dollar expense.
Some of these ideas will work in any situation. They are based fundamentally on the principle that if you want a person to go in a specific direction ... give him a positive to move to and a negative to move from.